The 13-Week Cash Flow Forecast: Why Profitable Contractors Still Run Out of Money

Imagine a contractor whose jobs are all profitable on paper, who still spends a Friday deciding which supplier to pay late so payroll clears. Nothing is wrong with the work. The money the jobs earned has not arrived, and the money the business owes is due now. A 13-week cash flow forecast is the tool built for that gap: a weekly table that projects the bank balance one quarter ahead, far enough to see a shortfall while there is still time to arrange for it. The profit and loss statement says whether the work made money. The forecast says whether the business can pay its bills on the way to collecting it.

Why Profit and Cash Separate

Profit is measured on work earned; cash moves on its own calendar. A contractor pays crews weekly or biweekly, buys materials before installing them, and carries equipment and overhead every week, while the owner pays after the work is billed, reviewed, and approved, and may hold back retainage under the contract. Every active job sits somewhere in that gap between paying for the work and collecting for it. Several jobs in their gaps at the same time can leave a profitable company short of cash, and a growing company feels it more, because each new job opens a new gap before the last one closes.

The Lines in the Forecast

Each week of the forecast has the same structure:

1. Beginning cash. The bank balance carried from the prior week.
2. Collections. Cash expected to arrive that week: progress payments, service invoices, deposits, and retainage releases. Each is placed in the week the money is realistically expected, based on how that customer actually pays, not the week the invoice goes out.
3. Disbursements. Payroll on its cycle, subcontractor and supplier payments on their terms, overhead, insurance, equipment payments, and tax deposits, each in the week it is paid.
4. Financing. Draws on a credit line, repayments, or owner contributions, shown on their own line so the forecast separates the business’s operating cash from borrowed cash.
5. Ending cash. Beginning cash plus collections, minus disbursements, plus or minus financing. It becomes next week’s beginning cash.

A minimum cash buffer sits beside the table: the balance the business wants to keep for errors and surprises. Any week that falls below it is a week that needs a decision now.

A Full 13 Weeks

Here is a hypothetical forecast for a contractor starting with $50,000 in the bank, a $20,000 minimum buffer, and a working-capital line used to hold the balance at that buffer. Week 4 includes a large progress payment, week 8 another, and week 13 includes a $25,000 retainage release. All figures are in thousands of dollars. Interest and fees on the credit line are left out for illustration; in a real forecast they belong in disbursements, and they make each borrowing week slightly more expensive than the table shows.

Week	Beginning	Collections	Payroll	Subs and suppliers	Overhead and taxes	Line draw or (repayment)	Ending	Line balance
1	50	30	28	15	6	0	31	0
2	31	20	28	22	4	23	20	23
3	20	15	28	10	6	29	20	52
4	20	120	28	18	4	(52)	38	0
5	38	25	28	12	6	3	20	3
6	20	40	28	9	4	1	20	4
7	20	35	28	15	6	14	20	18
8	20	95	28	20	4	(18)	45	0
9	45	10	28	8	6	7	20	7
10	20	30	28	14	4	16	20	23
11	20	60	28	10	6	(16)	20	7
12	20	45	28	9	4	(4)	20	3
13	20	70	28	12	6	(3)	41	0

Across the quarter, collections total $595,000 and disbursements $604,000, so the business ends $9,000 below where it started, at $41,000, with the line repaid. The forecast shows three things a bank balance never would. The line has to carry $52,000 by week 3, before the week 4 payment arrives. Weeks 9 and 10 need $23,000 of borrowing even though the quarter as a whole is close to break-even. And the quarter only closes clean because the week 13 retainage release arrives on time.

Testing the Forecast Against a Late Payment

A forecast that only works if every customer pays on schedule describes a best case. Move the week 4 payment of $120,000 two weeks later, to week 6, and run the same rules:

Week	Ending cash	Line balance
4	20	102
5	20	123
6	20	4

The peak line balance rises from $52,000 to $123,000. If the credit line is smaller than that, the forecast has found the problem weeks before it arrives: the contractor can press for the payment, slow a supplier with agreement, hold a discretionary purchase, or arrange more credit while the bank still sees a healthy business. The value is not predicting the future exactly. It is seeing which weeks are tight and how much room there is.

Retainage and Change Orders Inside the Forecast

Retainage. Model it as its own collection line, placed in the week the contract’s release terms make it realistic, not as part of each progress payment. On Florida public work, the Florida retainage release rules set part of that timing. Treating billed work as fully collectible overstates every receipt by the retainage percentage and hides a shortfall that only appears at the end of the project.

Change orders. Work done before a change order is approved puts payroll and materials into disbursements immediately, while the matching collection cannot be billed until the change is signed. The forecast shows that gap as a dip. Getting change orders approved before the work, and billing them, is a cash improvement the contractor controls directly.

Billing cadence. A billing sent late pushes its collection late. Billing the full earned amount on time every cycle strengthens every collection line in the forecast. The work-in-progress report shows whether billing is running ahead of or behind the work; the forecast shows what those billing decisions do to the bank balance.

Keeping It Rolling

Each week, replace the oldest week’s projection with what actually happened, add a new thirteenth week, and compare the variance. A collection that keeps arriving later than forecast is a customer whose payment pattern needs a new assumption. A disbursement line that keeps running over is a cost that needs attention. Owners build and update the forecast themselves, or have an outside bookkeeper maintain it, such as Tide & Ledger, a Tampa Bay firm that lists contractors and trades among the businesses it serves. Either way, the forecast is only as good as the willingness to believe its tight weeks.

Buffers That Make a Tight Week Manageable

The forecast shows the gaps; it does not fund them. Two structural buffers do:

• Working capital. Cash held to cover the normal funding gap between paying for work and collecting for it. A company that grows its volume without growing that reserve runs tighter with every job it adds.
• A credit line arranged in advance. A line set up before it is needed can be drawn deliberately against a trough the forecast predicted, instead of being requested in the week the account is about to go negative.

Faster collections shrink every gap: invoice at each milestone without delay, follow up the day a payment is late, and settle small disputes that hold up otherwise payable invoices.

The Weekly Routine

Update actuals, roll the thirteenth week forward, check every week’s ending balance against the buffer, and run one late-payment scenario on the largest expected collection. Decide this week what to do about any week below the buffer. Done every week, the forecast turns payroll surprises into scheduled decisions.

This guide explains 13-week cash flow forecasting as general information, not financial or accounting advice. Payment terms, retainage, and financing depend on your contracts and lenders, so confirm the assumptions with a qualified accountant before relying on a forecast.