Thinking about a sabbatical, a slow season, or finally dropping the client that pays the bills so you can go all-in on your own thing? The question that actually matters isn't "how much do I have saved" — it's "how many months does that buy me." This calculator turns your current savings, your real monthly expenses, and any income still trickling in while you're off into a straight answer: how long your runway actually is, a more conservative version of that number, and the true monthly burn rate driving it.
How it works
Start with your net monthly burn — the rate your savings actually drain at, not your full expense total. That's monthlyExpenses − monthlyIncomeWhileOff: if nothing is coming in while you're off, burn equals your expenses in full; if you'll still pick up part-time work, a retainer client, or a partner's income, that offsets the burn dollar for dollar.
From there, runwayMonths = currentSavings ÷ netMonthlyBurn — how many months your current savings cover at that burn rate. Because plans slip and expenses spike, the calculator also reports a safe runway: a flat 80% of the raw number (runwayMonths × 0.8), so you have a built-in cushion instead of planning around a best-case timeline that assumes nothing ever goes sideways.
One guard matters here: if your income while off equals or exceeds your expenses, net burn drops to zero or goes negative — you're not spending savings down at all, you're holding steady or even growing them. A "months of runway" figure doesn't mean anything in that case, so the calculator reports a large placeholder instead of dividing by zero or a negative number; your net monthly burn output (which will read $0 or negative) is the number that actually tells the story.
Worked example
Say you've got $24,000 in savings, your monthly expenses run $4,000, and you're not expecting any income at all while you're off.
- Net monthly burn: $4,000 − $0 = $4,000
- Runway: $24,000 ÷ $4,000 = 6 months
- Safe runway: 6 × 0.8 = 4.8 months
Six months of runway is roughly 26 weeks (6 × ~4.345 weeks per month) — useful if you're thinking in weeks of a job search or a sabbatical rather than calendar months. Now suppose you land $1,000 a month in part-time work while you're off: net burn drops to $4,000 − $1,000 = $3,000, and that same $24,000 stretches to $24,000 ÷ $3,000 = 8 months of runway, with a safe estimate of 6.4 months. Even a modest trickle of income meaningfully extends how long you can stay off the clock.
How to interpret your result
Runway is the honest ceiling — how long your money lasts if everything goes exactly as planned and nothing costs more than you budgeted. Safe runway is the number to actually build a plan around: it assumes real life intrudes a little, whether that's a bill you forgot, a slower-than-expected return to paid work, or a month where the part-time income didn't show up. Treat the gap between the two as your margin for error, not as slack to spend.
Net monthly burn is worth watching on its own, separate from the runway figure. It's the rate you're actually depleting savings at, and it's the number to recheck any time your expenses or your side income changes — a $200 monthly retainer client can add real months to your runway without touching your savings balance at all.
This is deliberately not an emergency-fund calculator. An emergency fund is a target you save toward before something goes wrong — "get six months of essential expenses in the bank." This tool assumes you've already got savings and are looking at a planned gap — a sabbatical, a business launch, a slow season, a career pivot — and tells you how far that specific pile of cash actually goes given your specific spending and income. Different question, different tool.
Methodology & sources
netMonthlyBurn = monthlyExpenses − monthlyIncomeWhileOff. When net burn is positive, runwayMonths = round(currentSavings ÷ netMonthlyBurn, 2 decimals) and safeRunwayMonths = round(runwayMonths × 0.8, 2 decimals). When net burn is zero or negative (income while off covers or exceeds expenses), the calculator reports a large sentinel runway instead of dividing by a non-positive number, since savings aren't actually depleting in that case — the net monthly burn output, not the runway figure, is what tells you the real picture. The calculator requires monthly expenses greater than zero.
This tool doesn't model investment returns on savings left untouched, taxes on any income earned while off, or one-time costs (a health insurance gap, a relocation) that don't fit neatly into a flat monthly number — build those into your expense figure by hand if they apply. For the broader discipline of separating essential cash-flow planning from day-to-day business decisions, the U.S. Small Business Administration's guide to managing your business finances is a solid starting point, even though it's written for small-business owners generally rather than freelancers taking planned time off specifically.