13-week cash runway calculator
How do I know if my business will run low on cash?
Build a 13-week cash forecast: start with the cash in the bank today, add the money you expect to land each week, subtract what you expect to pay out, and carry the balance forward. The week with the lowest closing balance is your pinch point, and dividing your cash by your typical weekly shortfall gives your runway in weeks. For example, $6,000 in the bank with $300 more going out than coming in each week is about 20 weeks of runway. If you make US estimated tax payments, the fourth 2026 payment is due January 15, 2027, which falls inside a 13-week window that starts in late October.
| Week | What | Amount ($) | In or out |
|---|---|---|---|
| Cash at the end of week 13 | $4200.00 |
| Lowest week: week 8 (Dec 14) | $2700.00 |
| First week below your $2000.00 floor | None in 13 weeks |
| First week below $0 | None in 13 weeks |
| Runway at typical weekly burn | 20.0 weeks |
| Week | Starts | Opening | In | Out | Closing |
|---|---|---|---|---|---|
| 1 | Oct 26 | $6000.00 | $2500.00 | $2800.00 | $5700.00 |
| 2 | Nov 2 | $5700.00 | $2500.00 | $2800.00 | $5400.00 |
| 3 | Nov 9 | $5400.00 | $2500.00 | $2800.00 | $5100.00 |
| 4 | Nov 16 | $5100.00 | $2500.00 | $2800.00 | $4800.00 |
| 5 | Nov 23 | $4800.00 | $2500.00 | $3700.00 | $3600.00 |
| 6 | Nov 30 | $3600.00 | $2500.00 | $2800.00 | $3300.00 |
| 7 | Dec 7 | $3300.00 | $2500.00 | $2800.00 | $3000.00 |
| 8 | Dec 14 | $3000.00 | $2500.00 | $2800.00 | $2700.00 |
| 9 | Dec 21 | $2700.00 | $5500.00 | $2800.00 | $5400.00 |
| 10 | Dec 28 | $5400.00 | $2500.00 | $2800.00 | $5100.00 |
| 11 | Jan 4 | $5100.00 | $2500.00 | $2800.00 | $4800.00 |
| 12 | Jan 11 | $4800.00 | $2500.00 | $2800.00 | $4500.00 |
| 13 | Jan 18 | $4500.00 | $2500.00 | $2800.00 | $4200.00 |
Cash basis: enter money when it actually lands in or leaves the bank, not when you invoice. Weeks below your floor are shaded. Runs in your browser; nothing is sent anywhere.
Last verified October 26, 2026 against IRS Form 1040-ES (2026), Estimated Tax for Individuals (PDF), SBA: Manage your finances. Fee change tracker · How we verify
Why 13 weeks?
Thirteen weeks is one quarter. It is short enough that you can name most of the money coming in and going out, and long enough to show quarterly bills (insurance, estimated tax, sales tax filings) and slow seasons before they arrive. A monthly profit report cannot show you a bad week; a weekly cash forecast can.
Cash, not profit
Enter money when it actually hits or leaves the bank. The SBA explains that the cash method records a sale only once payment has been received, which is what a cash forecast needs: an invoice you sent in week 2 that gets paid in week 6 belongs in week 6. That is also why a profitable business can still run short of cash.
What to put in
| Cash in | Cash out |
|---|---|
| Customer payments by the week you expect them to clear | Rent, utilities, phone, software subscriptions |
| Platform payouts (Etsy, Shopify, Square, Stripe, PayPal, Gumroad, Lemon Squeezy), net of fees | Payroll and your own draws |
| Deposits on booked jobs | Materials, inventory and supplies |
| Loan or line-of-credit draws (if any) | Loan payments, card bills, insurance renewals |
| Refunds owed to you | Tax payments, such as the January 15, 2027 estimated tax payment (your own amount) |
Worked example
A one-person cleaning business has $6,000 in the bank, about $2,500 a week coming in and $2,800 going out. That is a $300 weekly shortfall, roughly 20 weeks of runway. Add a $900 insurance renewal in week 5 and a $3,000 client payment in week 9, and the calculator shows the lowest week is week 8 at $2,700, just before the big payment arrives. If that client pays two weeks late, in week 11, the balance drops to $2,100 in week 10, barely above a $2,000 floor. That is the week to chase the invoice or move the insurance payment.
Questions
What is a 13-week cash flow forecast?
A week-by-week plan of the cash you expect to receive and pay over the next 13 weeks (one quarter), with each week's closing balance carried into the next. It shows the lowest week before it happens.
How do I calculate cash runway?
Divide the cash you have today by your average weekly (or monthly) shortfall, the amount by which cash out exceeds cash in. $6,000 with a $300 weekly shortfall is about 20 weeks. If cash in covers cash out, you are not burning cash.
How much cash should a small business keep on hand?
There is no single official number. Pick a floor that covers your fixed bills for a few weeks and the biggest one-off bill you expect, then use the forecast to see whether you stay above it.
Should I include estimated tax payments?
If you make them, yes, as cash out in the week you pay. IRS Form 1040-ES (2026) lists the 2026 due dates as Apr 15, Jun 15, Sep 15 2026; Jan 15 2027. This tool does not calculate the amount; ask a tax professional what you owe.
Does this replace bookkeeping?
No. Bookkeeping records what happened; a cash forecast plans what is about to happen. Update the forecast each week with actual balances.
General information, not tax, legal or accounting advice. Rates change: check the linked official source before you rely on a number. Not yet reviewed by a CPA or EA.
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