Second Job Calculator
Updated November 2026 · Free · No sign-up
Calculate whether a second job is worth it — the extra income lands at your MARGINAL tax rate, plus commute/childcare costs, divided by the real extra hours: the honest hourly rate of moonlighting.
Quick answer: Second-job dollars are your highest-taxed dollars: at a 22% federal + 7.65% FICA + 5% state marginal stack, a $600/week side job nets ~$390 — and after $40 of costs, 15 hours of work pays $23/hour real, not the advertised $40.
Why Second-Job Math Differs
Your main job eats the tax-free allowances and low brackets — every second-job dollar starts at your marginal rate. Mechanically: the US second W-4 withholds poorly without the multiple-jobs box (year-end surprises); the UK assigns BR code (flat 20%) to job two (code math); India clubs them at slab with one 87A rebate. Same principle everywhere: marginal, not average.
Worked Examples
Example 1 — retail evenings. $600/wk gross at 34.65% marginal = $392 net − $40 costs = $352 ÷ 15 hrs = $23.50/hour real — worth it against a $0 alternative, weak against overtime at your main job paying 1.5x marginal-adjusted.
Example 2 — the OT comparison. Main-job overtime at $45 (1.5 × $30) nets $29.40 at the same marginal stack — beating the side job per hour WITHOUT commute. Check OT availability before adding employers (OT tax math).
Example 3 — benefit cliffs. Extra income near EITC/benefit phase-outs or the UK child-benefit taper can face effective rates of 50-70% — the marginal field above accepts the ugly truth.
Alternatives Scoreboard
Rank by real hourly: main-job overtime (no commute, 1.5x) → raise negotiation (infinite hourly for hours invested) → freelancing at proper rates (deductions help) → W-2 second job (marginal everything) → gig apps (marginal taxes AND vehicle costs). The second job wins mainly on availability and separation-from-main-employer — price it knowingly. Watch moonlighting clauses in your primary contract; approval beats discovery.
Frequently Asked Questions
How much tax do I pay on a second job?
Your full marginal stack — bracket + FICA/NI + state — on every dollar, since job one consumed the allowances; commonly 30-40%+.
Why did my second job create a tax bill?
Withholding systems treat each job as your only one — the US multiple-jobs W-4 box or UK BR code fixes it; otherwise April reconciles painfully.
Is overtime better than a second job?
Usually — 1.5x pay, zero extra commute, one employer; a side job must beat your OT’s net hourly to make sense.
Do benefits change the math?
Yes — phase-outs (EITC, subsidies, UK child benefit) can push effective marginal rates past 50%; use the real combined rate above.
Can my employer stop me moonlighting?
Contracts often require disclosure/approval, especially for competitors or conflicts — check before, not after.
✓ Formula verified • Last updated: November 3, 2026