"When can I quit my job?" is the question every side hustler eventually asks, and most people answer it with a vibe instead of a number. This calculator gives you the number: how many months it takes your side income to compound its way up to a target salary, given the growth rate you're actually seeing month to month. It won't tell you when to quit — that's a runway and risk-tolerance question, not a math question — but it will tell you, honestly, whether "six more months" is a plan or a hope.
How it works
The engine treats your side-hustle income the way a bank treats compound interest, just running in your favor. Start with your current monthly net income, grow it by your entered growth rate every month, and check each month whether it's crossed your target. The number of months it takes to cross that line is your answer.
Two edge cases matter more than the main formula. First, if your current income already meets or beats your target, the calculator reports zero months — you don't need to wait on math you've already won. Second, if your growth rate is 0% (or you leave it there), the calculator can't compute a finite crossing point, because flat income never catches a higher target no matter how much time passes. Rather than show an error or a meaningless "Infinity," it reports a sentinel value of 999 months — a clear signal that at this growth rate, on this trajectory, the target isn't reachable at all. That's not a bug; it's the calculator being honest about a genuine math dead end.
The tool also projects where your current trajectory puts you 12 months out, compounding your current income at your entered rate for a year. That number is worth comparing against your target directly — it's a faster gut-check than counting months.
Worked example
Start with the defaults: $1,500 a month in current side-hustle net income, a 8% month-over-month growth rate, and a $5,000 target monthly income (a rough stand-in for a salary plus benefits).
- Ratio to close: $5,000 ÷ $1,500 = 3.33× your current income
- Growth multiplier per month: 1.08×
- Months needed: log(3.33) ÷ log(1.08), rounded up = 16 months
- Projected income in 12 months: $1,500 × 1.08¹² ≈ $3,777.26 — closer, but not there yet at the one-year mark
Sixteen months is over a year of sustained 8% monthly growth, which is a genuinely aggressive pace to hold for that long — worth sitting with before you treat it as a plan. Drop the growth rate to something more typical, like 4%, and the same $1,500-to-$5,000 gap stretches to roughly 31 months instead. The month count is extremely sensitive to the growth rate you assume, which is exactly why the next section matters.
How to interpret your result
Treat the months-to-replace figure as a floor, not a promise. It assumes your growth rate holds perfectly steady every single month, with no slow season, no client churn, no algorithm change if you're creator-income-based, and no plateau once you exhaust your easiest customers. Real side-hustle growth is lumpy — a launch month spikes, the next two flatten out — so the honest way to use this number is to re-run it monthly with your actual trailing growth rate, not to treat month 16 (or whatever you get) as a locked-in date on a calendar.
If you see the 999-month sentinel, don't read it as "never" — read it as "not on this trajectory." It means your current growth rate literally isn't enough, which is useful information: it's telling you to find a lever (higher rates, a new offer, more clients) rather than to wait passively for compounding to bail you out at 0% growth.
And whatever month the calculator lands on, that's the month your side income could theoretically cover your target — not the month it's safe to hand in notice. Build a runway buffer (three to six months of expenses saved) before you quit, and confirm the income actually held for a couple of consecutive months rather than jumping the day you first cross the line.
Methodology & sources
The core formula solves for n in current × (1 + rate)ⁿ = target, which rearranges to n = log(target ÷ current) ÷ log(1 + rate), then rounds up to a whole month since a partial month doesn't count as "replaced." The 12-month projection uses the same compounding formula directly: current × (1 + rate)¹². This is standard compound-growth math — the same mechanism behind Compound Annual Growth Rate (CAGR), just applied to a monthly income stream climbing toward a target instead of an investment climbing toward a future value.
The calculator deliberately does not model volatility, seasonality, or growth deceleration — all real and all common in side-hustle income — because doing so honestly would require data about your specific business the tool doesn't have. Use the output as a single trajectory under one assumption, and re-check it as your actual numbers come in.