Headcount & Compensation Planner: Model Every Hire's Fully-Loaded Cost by Month

The problem this kills

Personnel cost is the biggest line in almost every budget, and it's the one teams model in the most fragile way: a sprawling spreadsheet where every planned hire is a row, every month is a column, and a thicket of hand-built formulas tries to spread one salary across the calendar, add employer taxes and benefits, prorate the month someone actually starts, and bump pay on a raise date. One mistyped start date or a load rate that didn't get dragged to the new row, and the whole budget is off by tens of thousands of dollars — and nobody catches it until the variance shows up three months later.

It gets worse when the plan changes, which it always does. A role gets backfilled, a start date slips a quarter, a planned hire gets cut, leadership approves two new reqs in a board meeting. Each change means re-dragging formulas and hoping nothing broke. And because the "approved headcount" lives in the same editable workbook as the working draft, there's no clean line between what leadership actually signed off on and what someone has been quietly tweaking since.

Headcount and comp planning deserves to be a real, governed tool — one that computes the loaded cost correctly every time, prorates and ramps automatically, and locks the approved plan before it flows into the budget.

What you'll build

A simple internal web app for your FP&A and HR partners. You enter your roster — current employees and planned/open roles — each with a title, department, salary, start date, an employer-load percentage, and a raise schedule. The tool computes each role's fully-loaded cost month by month: it prorates the month a person starts (or terminates), layers on employer taxes and benefit loads, and steps pay up on each raise date.

It rolls every role up into the personnel-cost lines of your budget and a headcount-by-month report (heads by department, by month, planned vs. existing). Finance and HR leadership review the plan — the new-hire additions, the start dates, the load assumptions — and approve it. Only an approved, versioned plan can be exported into the budget. When the plan changes, you version it, so you always know exactly what leadership signed off on and what's still a draft.

What's inside the Implementation Plan

The downloadable plan is a step-by-step file you paste into an AI coding agent. It opens by interviewing you about your business — how you plan headcount today, what your roster actually looks like and what the columns are named, your employer-tax and benefit load rates, how raises and promotions work, how you handle backfills and terminations, and the messy exceptions (mid-month starts, contractors, bonuses, multiple raise events). It reflects a short tailored spec back to you and gets your thumbs-up before it builds anything, so the model matches how your company actually staffs and pays — not a generic template.

From there it walks the agent through the data model, the roster import, the month-by-month loaded-cost engine (proration, taxes, benefits, raises), the headcount roll-up, the leadership approval gate, plan versioning, and the CSV exports. Every step ends with a ready-to-copy prompt. There's a full "No API yet?" path that uses a Google Sheet / CSV as the roster source and produces clean CSV exports — the personnel-cost lines and a headcount-by-month report — in the exact columns your budget tool expects, so you can build and use the whole thing this weekend regardless of what HRIS or planning system you're on.

The governance it includes (this is the point)

Comp data is sensitive and the headcount plan feeds the budget, so the controls aren't optional. The plan builds in login so only your finance and HR team can use it, row-level security so you only ever see your own organization's salary data, a complete audit trail of who changed which role or rate and who approved which plan version, a hard human-approval gate so no plan — and no new-hire addition — flows into the budget until finance/HR leadership signs off, and duplicate guards (dedupe on role id) so the same role can't be counted twice when you re-import the roster.

Who it's for

FP&A analysts and HR business partners who own headcount and labor-cost planning, plus finance-owning founders building their first real personnel budget. If you can describe how your roster is laid out, what your load rates are, and how raises and backfills work at your company, you can build this.

You've got this — start with the plan, paste the first prompt, and answer the interview. You'll have your first fully-loaded headcount plan on screen before the weekend's out.