Emergency Fund Calculator
How many months should an emergency fund cover when income is irregular?
Cover 3 + 12 × CV months of essential costs, where CV is the coefficient of variation of your recent monthly net income — rounded up and capped between 3 and 12, so the flat “3–6 months” is only right when income is fairly steady. The freelance sample year below swings at CV 0.53 and needs 10 months of cover: a $35,025.00 fund at $3,502.50 a month.
The standard advice — “save 3–6 months of expenses” — assumes your income is the same every month. If yours isn’t, the right cushion depends on how hard it swings. Type your last months of net income and this page sizes the fund from your own volatility: months of cover, the target in dollars, how long what you have would last, and how many months until you’re funded.
| Volatility (CV = SD ÷ average) | 0.53 | Volatile. Your buffer has to do real work. |
|---|---|---|
| Months of cover your swings call for | 10 | Rule: MIN(12, MAX(3, ROUNDUP(3 + 12 × CV))) |
| What one month costs to run | $3,502.50 | self-paycheck $1,652.50 + your fixed monthly costs |
| Your cushion target | $35,025.00 | 10 months × $3,502.50 (self-paycheck + fixed costs) |
| How long you’d last today at zero income | 4.1 | what you have ÷ what one month costs to run |
| Left to save | $20,825.00 | target − what you already have set aside |
| Months until fully funded | 35 | at $600.00 added per month, rounded up to whole months |
| Your worst logged month | $640.00 | What the buffer absorbs in a month that bad: $2,862.50 |
Runs on our server with the same Buffer & Runway rules as our Irregular Income Toolkit, verified against an independent model. Your numbers are used for this one answer and never stored.
This page is one calculation from the toolkit. The workbook logs income as you earn it, keeps the target current, adds the tax set-aside and shows buffer, runway and self-paycheck on one dashboard.
See the spreadsheet → $29How this calculator works
It reads your logged months and works out three things. First, your self-paycheck: the 25th percentile of your months — a floor you clear in roughly 9 months out of 12. Second, your volatility: the coefficient of variation (standard deviation ÷ average), which turns “my income is all over the place” into one number. Third, the months of cover: 3 + 12 × CV, kept between 3 and 12 — a steady salary lands at 3 months, feast-and-famine income at 12. The target is those months times what one month costs to run (self-paycheck + fixed costs).
Everything runs on our server with the exact rules of our paid workbook — verified against an independent model, down to the cent — and nothing you type is stored. That is also why the maths is not in the page source: the calculation is live, the formulas stay home.
Why not a flat “3–6 months”?
Because the same monthly costs are a different risk on a salary than on freelance income that swings between $640 and $5,120 — the sample year above does exactly that. The flat advice prices both the same. Sizing by volatility means a steady earner is not told to over-save, and a volatile earner is not left with a cushion that dies in the first bad quarter. The floor of 3 months is exactly the classic advice — it is what the rule falls back to when your income barely moves.
Further reading
Frequently asked questions
Why does it ask for my income months instead of my expenses?
It asks for both. Fixed costs set part of what a month costs; your income months set how many of those months you need to hold. Two people with identical spending need different cushions if one is salaried and the other invoices — the swings, not the spending, are what the flat “3–6 months” advice ignores.
My income is the same every month — is this still for me?
Yes, and the answer gets simpler: with no swings the volatility is near zero and the rule lands on its 3-month floor — the classic advice. You still get the target in dollars, your runway today and the months-to-funded countdown.
What counts as fixed monthly costs?
What you would still pay in a bad month: rent or mortgage, utilities, insurance, minimum debt payments, the subscriptions you would actually keep. Not day-to-day spending — the self-paycheck part of the formula covers that.
Do you store my numbers?
No. The form sends them to our server for this one calculation, the answer comes back, and nothing is written down — no account, no cookie with your figures, no log of amounts. The only thing recorded is an anonymous “someone used the calculator” counter.
