I built a freelance rate calculator with Next.js

Source: Dev.to

Here’s the maths most calculators get wrong Most freelance rate calculators are wrong. Not buggy — conceptually wrong. They take your income goal, divide by hours, and hand you a number that will quietly lose you money all year. I got tired of explaining the correct calculation to freelancer friends, so I built a tool that does it properly. Here’s the logic behind it, and a bit about how I built it. The typical calculator does this: hourly_rate = annual_income_goal / annual_hours_worked

So if you want $80,000 and work 2,080 hours a year (40 × 52), it tells you to charge ~$38/hr. This is wrong in three separate ways. Your income goal is a net number — what you want to keep. But you’re taxed on gross. So the first correction is grossing up: const grossIncome = netTarget / (1 - taxRate); // $80,000 / (1 - 0.28) = $111,111

That’s already a $31,000 gap the naive formula ignores. This is the big one. Freelancers bill roughly 55–65% of their working hours. The rest is admin, proposals, invoicing, sales calls, and learning. const totalHours = weeksWorked * hoursPerWeek; // 46 * 40 = 1840 const billableHours = totalHours * billableRatio; // 1840 * 0.6 = 1104

So your real billable capacity isn’t 2,080 hours. It’s closer to 1,104. Pricing on the wrong denominator is how people end up working 50-hour weeks and still missing their income target. Software, hardware, insurance, courses — all real costs that need covering before you pay yourself: const totalNeeded = grossIncome + annualExpenses;

Putting it together: function minimumRate({ netTarget, taxRate, expenses, weeks, hoursPerWeek, billableRatio }) { const gross = netTarget / (1 - taxRate); const totalNeeded = gross + expenses; const billableHours = weeks * hoursPerWeek * billableRatio; return totalNeeded / billableHours; }

minimumRate({ netTarget: 80000, taxRate: 0.28, expenses: 8000, weeks: 46, hoursPerWeek: 40, billableRatio: 0.6 }); // ≈ $107/hr — not $38/hr

That’s a 2.8x difference from the naive calculation. On a full year, the gap between charging $38 and $107 is enormous. The tool is a Next.js 14 app (App Router) deployed on Vercel. The calculator itself is a single client component using useState for the inputs and useMemo for the derived rate — no backend needed, all the maths runs in the browser. The interesting architecture decision was programmatic SEO. Rather than one page, I generate static pages for every profession × country combination using generateStaticParams: export async function generateStaticParams() { return COUNTRIES.flatMap(country => PROFESSIONS.map(profession => ({ country, profession })) ); }

That turns 8 professions and 6 countries into 48 statically-rendered pages, each targeting a specific long-tail search like “freelance developer rate in Australia” — all built at deploy time, all served from the edge. Market benchmark data lives in plain JSON objects keyed by profession, with a currency multiplier applied per country. No database, no CMS — just static data and static rendering, which keeps it fast and free to host. The live tool is at freelancecalculator.net — free, no signup. Set your currency, enter your numbers, and it shows your minimum rate, a recommended rate with a 20% buffer, and how you compare to market benchmarks. If you’re a freelance dev and you’ve never run your rate through the corrected formula, it’s worth 60 seconds. Your number might be higher than you think.