new sub page paradigm
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samantha42
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<meta charset="UTF-8" />
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<meta name="viewport" content="width=device-width, initial-scale=1.0" />
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<title>FP&A Budgeting Engine — Samantha Vero Friis</title>
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<link rel="preconnect" href="https://fonts.googleapis.com" />
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<link href="https://fonts.googleapis.com/css2?family=DM+Mono:wght@300;400;500&family=Libre+Caslon+Text:wght@400;700;800&family=Syne:wght@400;700;800&display=swap" rel="stylesheet" />
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<link rel="stylesheet" href="/static/style/styles.css" />
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<style>
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/* ── Page-specific layout ── */
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header { padding: 2.4rem 0 2rem; }
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main { padding: 3rem 0 5rem; }
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.prose-block { max-width: 660px; }
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pre {
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font-family: "DM Mono", monospace;
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font-size: 0.78rem;
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line-height: 1.8;
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background: var(--surface);
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border: 1px solid var(--border);
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padding: 1.4rem 1.6rem;
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overflow-x: auto;
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margin: 1.6rem 0;
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color: #c8c8c0;
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}
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/* stat cards at top */
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.cards { margin: 2rem 0 2.5rem; }
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footer {
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border-top: 1px solid var(--border);
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padding: 1.6rem 0;
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display: flex;
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justify-content: space-between;
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align-items: center;
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font-size: 0.7rem;
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color: var(--muted);
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}
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footer a { color: var(--muted); text-decoration: none; }
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footer a:hover { color: var(--accent); }
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@media (max-width: 560px) {
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.cards { grid-template-columns: 1fr 1fr; }
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}
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</style>
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</head>
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<body>
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<!-- ── HEADER ── -->
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<header>
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<div class="container">
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<a class="back" href="/">← back</a>
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<div class="tag">project</div>
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<h1>FP&A <span>Budgeting Engine</span></h1>
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<div class="byline">
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<span>Samantha Vero Friis</span>
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<span style="color:var(--muted)">Go · REST API · Finance</span>
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<span style="color:var(--muted)">March 2026</span>
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</div>
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</div>
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</header>
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<!-- ── STAT CARDS ── -->
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<div class="container">
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<div class="cards">
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<div class="card">
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<div class="card-label">Language</div>
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<div class="card-value" style="color:var(--accent)">Go</div>
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</div>
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<div class="card">
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<div class="card-label">Database</div>
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<div class="card-value" style="color:var(--accent)">SQLite</div>
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</div>
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<div class="card">
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<div class="card-label">Architecture</div>
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<div class="card-value" style="font-size:1.1rem;color:var(--accent)">REST API</div>
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</div>
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<div class="card">
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<div class="card-label">Infrastructure</div>
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<div class="card-value" style="font-size:1.1rem;color:var(--green)">Zero deps</div>
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</div>
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</div>
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</div>
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<!-- ── MAIN ── -->
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<main>
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<div class="container">
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<div class="prose-block">
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<p class="lead">
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A REST API for corporate budget management, actuals ingestion, and variance
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reporting — built to replace the manual Excel workflow that smaller finance
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teams still run every month. Single binary, no infrastructure, deploys anywhere.
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</p>
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<h2>The problem it solves</h2>
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<p>
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At companies below a certain size — typically below 500 employees, or without
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the budget for enterprise planning platforms like Anaplan or Adaptive Planning —
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the monthly FP&A close still runs on spreadsheets. Actuals are exported from
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the ERP, pasted into a workbook, and variances are computed by hand across
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departments and GL accounts. The process is slow, error-prone, and breaks the
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moment someone edits the wrong cell.
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</p>
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<p>
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Large enterprises have solved this with dedicated tooling. The gap is the
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mid-market: companies that have outgrown Excel but cannot justify a six-figure
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implementation project. This engine sits in that space — structured schema,
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versioned budgets, on-demand actuals ingestion, and instant variance reports
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with no pivot tables and no shared file conflicts.
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</p>
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<blockquote>
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The goal was not to build something clever.<br>
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It was to build something that solves a real problem<br>
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<span>finance teams in the mid-market actually have.</span>
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</blockquote>
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<h2>Stack</h2>
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<p>
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Most finance tooling is Python notebooks or Excel macros — useful for analysis,
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fragile in production. Go compiles to a single binary with no runtime
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dependencies, makes every error path explicit, and handles concurrency safely.
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SQLite was chosen over Postgres deliberately: for a tool running inside a
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finance team's environment, zero infrastructure matters. The database is a
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single file. Backups are a file copy.
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</p>
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<div class="table-wrap">
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<table>
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<thead>
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<tr>
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<th>Layer</th>
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<th style="text-align:left">Choice</th>
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<th style="text-align:left">Reason</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td class="ticker">Language</td>
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<td style="text-align:left">Go</td>
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<td style="text-align:left;color:var(--muted)">Single binary, no runtime, explicit errors</td>
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</tr>
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<tr>
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<td class="ticker">Routing</td>
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<td style="text-align:left">net/http (stdlib)</td>
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<td style="text-align:left;color:var(--muted)">No deps; method+path routing since Go 1.22</td>
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</tr>
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<tr>
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<td class="ticker">Database</td>
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<td style="text-align:left">SQLite</td>
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<td style="text-align:left;color:var(--muted)">Zero infrastructure, file-based, ships with binary</td>
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</tr>
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<tr>
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<td class="ticker">Schema</td>
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<td style="text-align:left">Auto-migrated</td>
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<td style="text-align:left;color:var(--muted)"><code>CREATE TABLE IF NOT EXISTS</code> on startup</td>
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</tr>
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</tbody>
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</table>
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</div>
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<h2>API surface</h2>
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<p>
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Three resource groups. Budgets support full CRUD by department, GL account,
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fiscal period, and version. Actuals are ingested via a single upsert endpoint
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— idempotent by period, department, and GL code, designed to accept ERP
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JSON exports directly. Variance endpoints return computed reports immediately.
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</p>
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<pre>POST /api/v1/budgets Create a budget line
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PUT /api/v1/budgets/{id} Update amount or notes
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DELETE /api/v1/budgets/{id} Remove a budget line
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POST /api/v1/actuals/ingest Upsert an actual (idempotent)
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GET /api/v1/variance Full variance report
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GET /api/v1/variance/alerts Lines exceeding threshold
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GET /api/v1/health Returns 200 if DB is reachable</pre>
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<p>
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Variance endpoints accept <code>year</code>, <code>period</code>,
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<code>dept</code>, <code>version</code>, and <code>threshold</code>
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as query parameters.
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</p>
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<h2>Finance concepts implemented correctly</h2>
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<p>
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<strong style="color:var(--text)">Favourability logic.</strong> Whether a
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variance is good or bad depends on account type. Revenue accounts are
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favourable when actuals exceed budget; cost accounts when actuals come in
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under. The engine handles both via a <code>favour_high</code> flag per GL
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account — a distinction generic reporting tools consistently leave to manual
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configuration.
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</p>
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<p>
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<strong style="color:var(--text)">Budget versioning.</strong> Original budget
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and up to three forecast revisions are stored separately, enabling a full
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budget vs. forecast vs. actual three-way comparison without overwriting
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history — the standard FP&A reforecast workflow.
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</p>
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<p>
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<strong style="color:var(--text)">GL account typing.</strong> Accounts are
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typed as <code>revenue</code>, <code>cogs</code>, <code>opex</code>,
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<code>capex</code>, or <code>headcount</code>. This drives the P&L
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rollup structure and the favourability logic together, reflecting how an
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actual chart of accounts is structured.
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</p>
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<p>
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<strong style="color:var(--text)">Fiscal period decoupling.</strong> Periods
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are stored as integers 1–12, decoupled from calendar months — required for
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any company not on a January fiscal year.
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</p>
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<h2>Example output</h2>
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<p>
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Engineering department, FY2024 P09. Cloud infrastructure came in under budget.
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Consulting exceeded by 51%.
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</p>
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<div class="table-wrap">
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<table>
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<thead>
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<tr>
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<th>GL</th>
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<th>Description</th>
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<th>Budget</th>
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<th>Actual</th>
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<th>Var %</th>
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<th>Status</th>
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</tr>
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</thead>
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<tbody>
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<tr>
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<td>6100</td>
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<td style="text-align:left;color:var(--text)">Salaries & Wages</td>
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<td>4,200k</td>
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<td>4,380k</td>
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<td class="down">−4.29%</td>
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<td class="down">unfavourable</td>
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</tr>
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<tr>
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<td>6500</td>
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<td style="text-align:left;color:var(--text)">Consulting & Contractors</td>
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<td>450k</td>
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<td>680k</td>
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<td class="down">−51.11%</td>
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<td class="down">unfavourable</td>
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</tr>
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<tr>
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<td>5000</td>
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<td style="text-align:left;color:var(--text)">Cloud Infrastructure</td>
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<td>850k</td>
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<td>791k</td>
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<td class="up">+6.94%</td>
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<td class="up">favourable</td>
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</tr>
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</tbody>
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</table>
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</div>
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<h2>Running it</h2>
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<pre>git clone https://git.samantha42.xyz/samantha/FPandA-Engine
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cd FPandA-Engine
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cp .env.example .env
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go mod tidy
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go run ./cmd/server
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# → http://localhost:8080
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# → fpa.db created on first run</pre>
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<p>
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Two environment variables: <code>DB_PATH</code> (use <code>:memory:</code>
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for tests) and <code>PORT</code>. Demo seed data for Engineering, Sales,
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and Marketing is included in <code>scripts/seed_demo.sql</code>.
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</p>
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<hr />
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<p>
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Source at
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<a href="https://git.samantha42.xyz/samantha/FPandA-Engine"
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style="color:var(--accent);text-decoration:none"
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target="_blank">git.samantha42.xyz/samantha/FPandA-Engine</a>
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</p>
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</div>
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</div>
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</main>
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<footer>
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<div class="container" style="display:flex;justify-content:space-between;width:100%">
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<a href="mailto:me@samantha42.xyz">me@samantha42.xyz</a>
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<span>© 2026 — All rights reserved</span>
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</div>
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</footer>
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</body>
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</html>
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