How to Build a 13-Week Cash Flow Forecast for Your Business

Most owners who call us about cash are not unprofitable. Their Profit and Loss says they made money, and they still had a Thursday when payroll was due, two big invoices had not been paid, and the bank balance was $9,000. The question they are really asking is: what will be in the account on each payday between now and the end of the quarter, and what do I do if the answer is "not enough"?

A 13-week cash flow forecast answers that in a spreadsheet you can build in an afternoon and update in thirty minutes a week.

Why 13 weeks, and what the sheet looks like

Thirteen weeks is one quarter: long enough to catch every payroll, every monthly bill, a quarterly tax filing and the coming seasonal dip, and short enough that you can name the invoices you expect to collect. A 12-month projection is a budget built on assumptions; a 13-week forecast is a list of transactions built on the AR aging and the bills already on your desk.

One column per week, starting with the current week, and these rows in order:

• Opening cash: the reconciled bank balance, not what the bank's app shows. Uncleared checks are already spent.
• Receipts by source: collections on existing invoices, deposits on new work, card payouts, financing already signed. Keep them separate so the variance review shows which one missed.
• Disbursements by category: payroll as one all-in number including the federal deposit, subcontractors and materials, rent, insurance, loans, credit cards, software, owner draws.
• Payroll and tax dates: every payday, the federal deposit that follows it, quarterly filings, sales tax and estimated tax. These are the rows that get missed, and they carry penalties.
• Tax reserve: a weekly transfer to a separate account, covered below.
• Ending cash: opening plus receipts minus disbursements, which becomes next week's opening, with your minimum cash floor underneath.

Where the inputs come from

Weeks 1 through 4 are built from documents, not guesses. The accounts receivable aging gives every open invoice by customer and age; put each one in the week you expect the check, based on how that customer actually pays. The accounts payable aging gives the vendor side. The payroll calendar gives paydays, and your deposit schedule says when the federal taxes leave: employers with $50,000 or less of employment tax in the lookback period deposit monthly by the 15th of the following month, and employers above that deposit semiweekly, within days of each payday, under the rules in IRS Publication 15.

The recurring charges come from three months of bank and card statements: anything that hit two of the three months goes on the sheet on its usual day. Weeks 5 through 13 use signed contracts and a run rate for the rest. The tax calendar gets its own table because the dates are fixed and the amounts are large. For a Florida employer that collects sales tax:

The sales tax rules are in the Florida DR-15 instructions and the estimate dates on Form 1040-ES; our guide to how quarterly estimated taxes work covers the amounts.

Handling uncertainty, and the tax-reserve line

The receipts row is where forecasts go wrong, because owners enter the invoice in the week it is due and the customer pays three weeks later. Weight each receipt by the probability it arrives that week. In our practice we start around 90% for a current invoice from a customer who pays on time, 70% for 30 to 60 days old, 40% for 60 days and older and 10% for anything in dispute. A $40,000 progress billing rated at 70% goes on the sheet at $28,000 in the expected week and $12,000 two weeks later.

The tax-reserve line exists because a pass-through business pays no income tax itself, but its owner does, and the cash comes from the business. Make it a fixed weekly transfer to a separate account, not a lump sum you hope to have in April. For most owners in the 22% to 24% federal brackets, 25% to 30% of net profit is the right order of magnitude; Florida's lack of a personal income tax is why it is not higher. Two things are not reserve items and are never a cushion: the federal payroll deposit and collected sales tax. The IRS can assess a responsible owner personally for unpaid withholding under the Trust Fund Recovery Penalty, "equal to the unpaid balance of the trust fund tax," and a late Florida sales tax return carries a penalty of 10% of the tax with a $50 minimum.

Worked example: a $2 million contractor with a hole in weeks 6 to 8

Take a residential remodeling contractor in Hillsborough County doing about $2 million a year, with 14 employees paid every other Friday and an all-in payroll of $22,000 per run including the federal deposit. The forecast starts the week of October 5, 2026 with a reconciled opening balance of $61,000 and a cash floor of $40,000, roughly two payrolls. "Other outflows" combines rent, the equipment loan, insurance, the credit card, overhead, the third-quarter RT-6 in week 4, owner draws of $8,000 a month and a $1,500 weekly tax-reserve transfer.

The quarter as a whole is fine: $524,000 in, $535,450 out, and the difference is mostly draws and the tax reserve. The problem is the middle. A kitchen-and-addition job finished in week 4, and its $28,000 retainage was scheduled for week 9 because that is when the owner assumed the final inspection would happen. The next job mobilized in week 6 with a $14,000 framing package paid on delivery, and Thanksgiving week collected almost nothing. Cash drops below the floor in week 7 and goes negative in week 8, with a payroll week next. None of it shows on the Profit and Loss, which is why profit does not equal cash.

The fixes, applied in this order, were all things the owner controlled:

1. Collect faster. The owner scheduled the final inspection for November 13 and sent the retainage invoice the same day, moving $28,000 from week 9 to week 7.
2. Re-time the outflows you control. The lumber supplier agreed to net-30 on the framing package, moving $14,000 from week 6 to week 10, and the owner's November draw moved from week 8 to week 10.
3. Leave the government's money alone. The federal deposit stayed inside the payroll number and the reserve transfer kept running.
4. Arrange the bridge before you need it. The $50,000 line of credit was confirmed in week 5 as a backstop; with the first two levers it was never drawn.

The revised forecast ends week 6 at $64,850, week 7 at $54,350, week 8 at $49,850 and week 9 at $43,150, above the floor throughout, and finishes the quarter at the same $49,550. Nothing about the business changed; the timing did, because the owner saw the problem five weeks early. If the same dip appears every quarter, the forecast is telling you something about pricing or overhead, not timing.

The weekly routine and the variance review

Every Monday, thirty minutes. Replace last week's forecast column with actual receipts and disbursements from the reconciled bank feed, and compare. Ask why for any line that missed by more than $5,000 or 10%. Receipts variances are almost always timing, and they should change your probability weight for that customer. Disbursement variances are almost always a forgotten annual item, such as the insurance renewal or the workers' comp audit true-up; add it to the recurring list.

Then roll the window: drop week 1, add a new week 13, and refresh weeks 1 to 4 from the current AR and AP agings. Update the estimated tax and sales tax lines at the same time, because both change with the quarter's results. If you still judge cash from the Profit and Loss, our guide to reading it explains what it cannot tell you.

What usually goes wrong

The first mistake is starting from the bank's displayed balance instead of the reconciled balance. The second is entering receipts at invoice due dates rather than expected collection dates. The third is forgetting the tax rows: a semiweekly deposit two days after payday, a sales tax payment on the 19th, or the January 15 estimate that lands right after a slow December.

The fourth is treating the tax reserve, collected sales tax or the payroll deposit as available cash when the week gets tight. The fifth is building the forecast once, feeling better, and never updating it.

When to get help

If your books are reconciled monthly and the AR aging is accurate, you can build and maintain this forecast yourself with the layout above. The owners who struggle are usually the ones whose bookkeeping is a month or more behind, because the opening balance and the aging are unreliable. In our practice the forecast is one of the first things we set up for outsourced back-office clients, alongside the AR follow-up and payables scheduling that make the numbers real.

If you are looking at a dip like that right now and want a second set of eyes on the levers, request a 20-minute fit call and bring your AR aging, your payroll calendar and the last bank statement. That is enough to build the first four weeks on the call.

Jenny Gao, CPA, EA

Founder of Balance Partners. Florida-licensed CPA and IRS Enrolled Agent with more than a decade of accounting and tax experience. Jenny writes and reviews every guide on this site. About Jenny

This article is general educational information for U.S. business owners and is not accounting, tax, legal, payroll or financial advice for your situation. Rules change and vary by entity, state and facts. Balance Partners, LLC does not provide audit, review or other attest services. Last reviewed September 14, 2026.