13-week cash flow forecast: how contractors see next Friday before it hits

Contractors don't run out of cash "on average." They run out on a specific Friday. A monthly view can show a fine month while the weekly view shows payroll on the 12th landing before the draw on the 25th. Below: what a 13-week forecast is, why weekly beats monthly in construction, how to build one step by step, a labeled contractor example, and the mistakes that make the grid lie.

What is a 13-week cash flow forecast?

Term	Meaning
13-week cash flow	A grid: one column per week for the next ~quarter
Cash in	Collections timed by when money actually lands — not invoice date
Cash out	Payroll, subs, suppliers, overhead, lumpy items — by the week they leave
Ending cash	Starting balance + in − out; the row that shows low-water marks early

Why 13 weeks? It's a full quarter — far enough to see a crunch while you can still act (pull a draw forward, stage a sub payment, tap the line), near enough that the numbers stay defendable instead of hopeful.

Why weekly, not monthly? Construction cash is lumpy in both directions. Big draws in, big sub payments out, payroll every week no matter what, and retainage trickling in months behind the work. A "profitable" quarter can hide two weeks of genuine crisis — the mechanics live on why profitable contractors run out of cash. Your P&L measures whether you're winning. The 13-week forecast measures whether you'll make payroll while you win.

Why contractors need a weekly forecast (not a monthly one)

1. Payroll is weekly; draws are not. The calendar mismatch is the product. Monthly totals can net fine while one Friday is underwater.
2. Retainage and slow AR don't show up as "profit problems." Cash you've earned but haven't collected still has to fund labor and materials. Track retainage as its own inflows with realistic release dates.
3. Under-billing and job borrow hide until cash breaks. A monthly WIP schedule shows which jobs are financing the owner; the 13-week forecast shows when that financing shows up as a low balance. Pair them.
4. Growth spends cash before it earns it. Mobilization, labor, and materials go out weeks before the first draw. The best backlog year is often the worst bank-balance year without a weekly view.
5. Bankers prefer a plan over an apology. Calling with a forecast and a fix in week one is a different conversation than calling after you've missed payroll.

Blackline Financial is construction-only bookkeeping and advisory for contractors and specialty trades (roughly $1M–$30M). We do not prepare tax returns. Clean books, monthly close, and cash-flow forecasting as part of CFO advisory live on services — every engagement starts with a DIG Diagnostic, and every package is custom-quoted.

How to build a 13-week cash flow forecast for a contracting business

This is the walkthrough behind searches like "how do I build a 13 week cash flow forecast for a contracting business." Spreadsheet or model — same steps. No template download is promised here; the process stands alone.

Step 1 — Start from reconciled cash, AR, and AP

Opening balance = the real bank (and any operating LOC) after reconciliations. Pull open invoices and open bills from books you trust. A forecast built on unreconciled accounts inherits every error into week 13. If the books aren't close-ready yet, fix that first (how we close).

Step 2 — Map cash in by source and realistic date

Inflow	How to time it
Pay app / draw collections	Already submitted → use actual customer pay behavior (45 days if they pay in 45), not the contract's "net 30"
Draws not yet submitted	From each job's billing schedule; put them in the week you'll submit, then add the collection lag
Retainage releases	Separate line; tie to realistic closeout / punch-list dates, not wishful ones
Deposits / other	New-work deposits, refunds; planned LOC draws labeled as borrowings, not "collections"

Unsigned work and hoped-for change orders stay out until they're real. The forecast is for cash you can defend.

Step 3 — Map cash out — the honest list

Outflow	Notes
Payroll + payroll taxes	Every week or two; immovable; first on the list
Subs and suppliers	AP due dates and known commitments, including pay-when-paid timing
Fixed nut	Rent, insurance, loan payments, software, fuel
Lumpy items people forget	Insurance audit true-ups, equipment purchases, owner distributions, quarterly estimated tax payments (we don't prepare returns — your CPA owns tax; you still need the cash reserved)

Step 4 — Build the weekly grid and read the ending-cash row

One column per week. Cash in on top, cash out below, ending cash at the bottom. That bottom row is the whole point — it shows low-water marks weeks before you hit them. Flag any week that goes negative or dips below your minimum operating cushion.

Step 5 — Update weekly and track forecast vs. actual

Thirty minutes, every Monday: replace last week's guesses with what happened, roll a new week 13 on. If week-one projections keep missing by 20%, fix the assumptions — that feedback loop is what makes the model sharp. A stale 13-week cash flow forecast is worse than none: confidence without accuracy.

Labeled example (illustrative only)

Example only — not a client case, not a quote. Specialty contractor, ~$8M run-rate, three active jobs, weekly payroll. Opening cash at the start of week 1: $200,000.

	Wk 1	Wk 2	Wk 3	Wk 4	Wk 5	Wk 6
Collections	$85K	$0	$210K	$0	$40K	$180K
Payroll	($52K)	($52K)	($52K)	($52K)	($54K)	($54K)
Subs & suppliers	($30K)	($95K)	($60K)	($110K)	($25K)	($70K)
Overhead & other	($18K)	($12K)	($15K)	($12K)	($38K)	($12K)
Ending cash	$185K	$26K	$109K	($65K)	($142K)	($98K)

Illustrative grid only. Not a client, not a result, not a quote.

How to read it:

• Weeks 1–3 — Solvent, but week 2 is already thin after a big sub pay and no collection.
• Weeks 4–6 — The story: a hole that exists today, visible a month early. Time to pull a draw forward, stage sub payments, or draw the line — while options still exist.
• Week 5 overhead spike — Stands in for a lumpy item (insurance true-up, equipment, distribution). Monthly averages hide it; weekly columns don't.

Seen in week one, that hole is a planning problem with half a dozen solutions. Discovered in week four, it's a crisis with two — and both are expensive.

Common mistakes that break a 13-week forecast

1. Using contract terms instead of payment behavior. Net-30 on paper and 52 days in practice will fake every collection column.
2. Putting hope in the grid. Unsigned bids, verbal change orders, and "the GC said they'd pay Friday" don't belong until they're documented.
3. Skipping retainage as its own line. Mixing it into "collections" makes the back half of jobs look healthier than they are.
4. Updating monthly (or never). The product is the weekly habit, not the first spreadsheet.
5. Building it on dirty books. Wrong AR/AP/cash → wrong everything. Pair the forecast with a monthly WIP and a real close — see contractor cash flow and WIP schedule.
6. Treating over-billed cash as free. Job borrow spent like profit shows up as a cliff when the back half of the job needs money and there's nothing left to bill (over/under billing).

FAQ

What is a 13-week cash flow forecast?

A week-by-week projection of cash in, cash out, and ending bank balance for the next 13 weeks (about one quarter). The ending-cash row is the early-warning system for payroll and sub payment crunches.

Why weekly instead of a monthly cash flow for contractors?

Construction cash is lumpy. Payroll is weekly; draws and collections aren't. A monthly total can look fine while a specific Friday is underwater. Weekly columns catch the timing gap.

How do I build a 13-week cash flow forecast for a contracting business?

Start from reconciled cash/AR/AP; time inflows by real pay behavior (including retainage); list outflows honestly (payroll first); build one column per week; update every Monday and compare forecast vs. actual. Full walkthrough above.

How is a 13-week forecast different from a WIP schedule?

A WIP schedule shows earned vs billed by job. The 13-week forecast shows cash by calendar week. You want both: WIP explains which jobs trap cash; the forecast explains when the bank account feels it.

Can Blackline build and maintain a 13-week cash flow forecast?

Yes — for construction businesses, as part of CFO advisory on top of clean books and a monthly close. Start at contact or review packages. We don't prepare tax returns.