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STWLTH
Free Tool

Side Income Impact Simulator

How much does a $500/mo side hustle actually accelerate your FIRE date? Models the after-tax stream (W-2 / 1099 / cash), how much you reinvest, and the honest per-hour trade-off if you enter weekly hours.

Baseline (Your Current FIRE Trajectory)
Current Portfolio$100,000

Total investments today — retirement accounts + taxable + HSA. Sets the starting pot for both baseline and accelerated paths.

Monthly Expenses$4,000

Your typical monthly spend today — used to compute the FIRE number as 25× annualized (12 × monthly).

Baseline Savings$24,000

Annual savings BEFORE the side income — from your day job. The side income is additive on top of this.

Expected Return %7%

Real (inflation-adjusted) annual return on invested savings. 7% is a common assumption for a diversified equity portfolio.

Side Income Stream
Monthly Amount$500

Gross monthly amount before tax. Uber shifts, freelance, Etsy sales — whatever the extra income stream pays before deductions.

Duration8 yr

How many years the stream runs. Side hustles rarely last forever — be honest about the sustainable horizon.

Starts Innow

Delay before the stream begins. Some users are still ramping up — pushing the start back reduces the compounding impact.

Reinvest %100%

What fraction of the after-tax side income you actually invest. Set to 0% to see the 'you gave up your weekends for zero FIRE benefit' case.

Tax Treatment
Your Marginal Rate
Filing Status
Tax Year
Hours per Week—

Set to reveal the per-hour verdict. Turns '$500/mo' into 'you're trading N hrs/wk for M FIRE months earned' — the honest-math kicker.

FIRE Multiplier25×

Your FIRE number as a multiple of annual spending. 25× (4% SWR) is standard. 20× for Lean, 30–33× for a more conservative Fat FIRE.

FIRE Impact of the Side Income
Months Earlier to FIRE
9.1 mo
how much sooner you hit FIRE by reinvesting the after-tax side income
Total After-Tax Earned
$31,404
gross $48,000, net after 35% effective tax across the run
The Verdict

Reinvesting the after-tax side income accelerates your FIRE date by 9.1 months — roughly 0.8 years of earlier retirement for $31,404 of after-tax income over the run.

How the math works. 1099 treatment applies SECA (15.3% on 92.35% of net earnings) plus your federal marginal rate, with the deductible half of SECA netted out. Federal only — no state tax. Monthly compounding at your expected return. FIRE number = 25× annualized monthly expenses.
Baseline vs. accelerated (with reinvested side income)
Baseline portfolioExtra from side incomeFIRE number
Yr 1
$136,068
Yr 2
$174,744
Yr 3
$216,215
Yr 4
$260,684
Yr 5
$308,368
Yr 6
$359,499
Yr 7
$414,326
Yr 8
$473,117
Yr 9
$532,104
Yr 10
$595,355
Yr 11
$663,178
Yr 12
$735,905
Yr 13
$813,889
Yr 14
$897,510
Yr 15
$987,176
Yr 16
$1,083,324
Yr 17
$1,186,423
Yr 18
$1,296,975
Yr 19
$1,415,518
Baseline vs. accelerated (with reinvested side income)
LabelBaseline portfolioExtra from side income
Yr 1132,0144,054
Yr 2166,3438,401
Yr 3203,15313,062
Yr 4242,62418,060
Yr 5284,94823,420
Yr 6330,33229,167
Yr 7378,99735,329
Yr 8431,18041,937
Yr 9487,13644,968
Yr 10547,13648,219
Yr 11611,47351,705
Yr 12680,46255,443
Yr 13754,43859,451
Yr 14833,76163,748
Yr 15918,81968,357
Yr 161,010,02673,298
Yr 171,107,82678,597
Yr 181,212,69684,279
Yr 191,325,14790,371

Estimation only. Not financial or tax advice. Federal tax modeling only — no state tax. 1099 self-employment approximation applies SECA (15.3% on 92.35% of net earnings) plus your federal marginal rate with half-SECA netted from the deductible portion. Actual filings depend on deductions, quarterly estimates, and business-expense treatment this tool does not model.

Estimation only. Not tax or financial advice. Federal-only tax modeling; state tax and business expenses are not included.