How to make a 13-week cash flow forecast

How do I make a 13-week cash flow forecast?

Start with today's bank balance. For each of the next 13 weeks (one quarter), list the cash you expect to come in, in the week it will actually land, and the cash going out: payroll, rent, loan and card payments, supplies, insurance, fees and tax payments on their due dates. Each week, opening balance + cash in − cash out = closing balance, which carries into the next week. The forecast's job is to show your lowest week before it happens, so you can chase invoices, move a purchase or line up funding in time. Update it every week: replace the past week with actuals and add a new week at the end.

Last verified October 28, 2026 against SBA: Manage your finances, SBA: Write your business plan (financial projections), IRS Form 1040-ES (2026), Estimated Tax for Individuals (PDF), IRS: Estimated taxes. Fee change tracker · How we verify

Why 13 weeks, and why weekly?

Thirteen weeks is one quarter (52 ÷ 4), long enough to see a slow season, a quarterly bill or a tax payment coming, and short enough that you can estimate each week with some confidence. Weekly matters because payroll, supplier bills and deposits land on specific days; a monthly total can look fine while one week in the middle goes negative. The SBA's business plan guidance makes a similar point for projections in general: for the first year, use quarterly, or even monthly, projections.

A cash forecast is different from a profit report. The SBA explains that the accrual method records a sale when it is made, while the cash method only records a sale once payment has been received. A 13-week forecast always works on the cash view: what matters is the week the money arrives or leaves your account.

What to include

Cash in	Cash out
Customer payments by expected pay date (use each client's real payment habits)	Payroll and payroll taxes, on pay dates
Platform payouts (Etsy, Square, Stripe, PayPal) on their deposit schedule, after fees	Rent, insurance, software and phone
Deposits on booked jobs	Supplies, materials and inventory purchases
Loan or line-of-credit draws (only if approved)	Loan, card and equipment payments
Owner contributions	Owner draws, and estimated tax payments on IRS due dates

For estimated tax, IRS Form 1040-ES lists the 2026 due dates as April 15, 2026, June 15, 2026, September 15, 2026, January 15, 2027, so a forecast made today should show the January 15, 2027 payment as a cash-out line. The IRS also says weekly, bi-weekly or monthly is allowed, as long as enough is paid by each due date, which can smooth a large quarterly payment into smaller weekly ones. The amount is yours to set; see how much to set aside for taxes.

A worked example

A made-up cleaning business with $6,000 in the bank and a $2,500 safety floor. The numbers are illustrative, not benchmarks.

Week	Opening	Cash in	Cash out	Net	Closing	Note
1	$6,000	$3,200	$2,800	$400	$6,400
2	$6,400	$3,400	$3,900	−$500	$5,900	Payroll + insurance
3	$5,900	$2,900	$2,700	$200	$6,100
4	$6,100	$3,600	$4,300	−$700	$5,400	Payroll + van repair
5	$5,400	$3,100	$2,900	$200	$5,600
6	$5,600	$3,300	$3,000	$300	$5,900
7	$5,900	$2,700	$3,600	−$900	$5,000
8	$5,000	$2,200	$2,600	−$400	$4,600	Holiday weeks, fewer jobs
9	$4,600	$2,400	$2,700	−$300	$4,300	Holiday weeks, fewer jobs
10	$4,300	$3,500	$2,900	$600	$4,900
11	$4,900	$3,300	$5,900	−$2,600	$2,300	Payroll + Jan 15 estimated tax (your amount)
12	$2,300	$3,400	$3,000	$400	$2,700
13	$2,700	$3,600	$2,800	$800	$3,500

The lowest week is week 11 at $2,300, and the first week under the $2,500 floor is week 11. Seeing that now leaves time to act: invoice the week 10 jobs promptly, push a non-urgent purchase past week 11, or spread the tax payment across earlier weeks. Run your own 13 weeks in the free 13-week cash runway calculator.

Keep it honest

Reconcile first. The opening balance should match the bank. The SBA lists receivables, payables, available cash, bank reconciliation, payroll among the tasks someone in the business should manage.
Use payment dates, not invoice dates. If a client usually pays in 30 days, put the cash 4 weeks after the invoice.
Be conservative on cash in. Count only booked work for the next few weeks; add a separate, lower line for expected new work.
Track forecast vs actual. Each week, note what was off. After a month or two your estimates get much tighter.

Questions

What is a 13-week cash flow forecast?

A week-by-week list of the cash you expect to receive and pay over the next 13 weeks (one quarter), with a running bank balance, so you can spot a cash shortfall before it happens.

How is a cash flow forecast different from a profit and loss?

A profit and loss shows whether you made money over a period; a cash forecast shows when money actually moves. The SBA notes the cash method only records a sale once payment has been received, which is the view a cash forecast uses.

How often should I update it?

Weekly. Replace the week that just ended with actual figures, add a new week 13, and adjust any estimates that turned out wrong.

Should I include estimated tax payments?

Yes, as cash out on their due dates. IRS Form 1040-ES lists April 15, 2026, June 15, 2026, September 15, 2026, January 15, 2027 for 2026. The IRS says weekly, bi-weekly or monthly is allowed, as long as enough is paid by each due date.

What should I do if a week goes below my floor?

Act early: invoice and follow up faster, ask for deposits on booked work, move non-urgent purchases, talk to suppliers about timing, or arrange a line of credit before you need it.

Do I need accounting software for this?

No. A spreadsheet works, as long as the opening balance matches your bank and you update it weekly.

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.