13-Week Cash Flow Forecast: How to Build It (With Template)

A business can finish the quarter with more cash than it started with and still come up short in week twelve. Every month-end balance looks fine, and then a tax payment, an insurance renewal, and a slow-paying client all land in the same two weeks.

A 13-week cash flow forecast finds that week before it arrives. By the end of this post you will be able to build one, read its low point, and keep it honest, using a full example for a small service business.

What a 13-Week Cash Flow Forecast Actually Is

A 13-week cash flow forecast is a week-by-week projection of the cash landing in and leaving your bank account over the next quarter. Fifty-two weeks divided by four is thirteen, so it covers one full quarter: long enough to see trouble coming, short enough to build mostly from invoices and bills you already know about.

It is not a budget and it is not a P&L. Revenue you billed but have not collected stays out, and so does depreciation. The FDIC and SBA’s Money Smart for Small Business guide to managing cash flow describes a cash flow projection as an estimate of future cash in and cash out. The 13-week version puts it in weekly buckets, because payroll and rent clear on specific days. If profit and cash still feel like the same thing, start with our post on the cash flow mistakes that kill small businesses.

Our post on cash flow forecasting mistakes explains why the rolling 13-week format works. This post is the build guide.

The Formula Behind Every Week

Ending Cash = Beginning Cash + Cash Receipts – Cash Disbursements

That line repeats thirteen times. Each week’s ending cash becomes the next week’s beginning cash, so a week-two error carries into every later week.

Beginning cash. Your actual bank balance today, minus checks and payments that have gone out but not cleared.

Cash receipts. Deposits you expect that week: customer payments, retainer drafts, loan proceeds. Place each one in the week the money arrives, based on how that customer actually pays.

Cash disbursements. Every dollar leaving the account, including card payments, loan payments, taxes, and owner distributions. Place each one in the week it clears.

Minimum cash floor. The balance you refuse to go below. It turns the forecast into a decision tool. Any week that ends below the floor needs an action attached.

Worked Example: A Four-Person Marketing Agency

The agency runs on monthly retainers plus project invoices. Months start in weeks 1, 5, and 9, so month three has five weeks.

Inputs:

Beginning cash: $39,000
Minimum cash floor: $30,000 (two payroll runs plus one month of rent, rounded up)
Retainer collections: $22,000 in the first week of each month and $14,000 in the second (weeks 1, 2, 5, 6, 9, 10)
Open invoices: $9,000 in week 2 and $7,000 in week 4
A $14,000 invoice due in week 9 from a client who reliably pays four weeks late, so it goes in week 13
New project collections: $5,000 in weeks 7, 11, and 13
Payroll including payroll taxes: $13,000 every other week (weeks 2, 4, 6, 8, 10, 12)
Contractors: $1,500 every week
Rent of $3,500 and software of $1,800 (weeks 1, 5, 9)
Loan payment: $1,850 (weeks 2, 6, 10)
Credit card payment: $4,000 (weeks 3, 7, 11)
Owner distribution to fund a quarterly estimated tax payment: $14,000 in week 11
Annual business insurance renewal: $7,200 in week 12

Week	Beginning cash	Receipts	Disbursements	Net	Ending cash
1	$39,000	$22,000	$6,800	$15,200	$54,200
2	$54,200	$23,000	$16,350	$6,650	$60,850
3	$60,850	$0	$5,500	($5,500)	$55,350
4	$55,350	$7,000	$14,500	($7,500)	$47,850
5	$47,850	$22,000	$6,800	$15,200	$63,050
6	$63,050	$14,000	$16,350	($2,350)	$60,700
7	$60,700	$5,000	$5,500	($500)	$60,200
8	$60,200	$0	$14,500	($14,500)	$45,700
9	$45,700	$22,000	$6,800	$15,200	$60,900
10	$60,900	$14,000	$16,350	($2,350)	$58,550
11	$58,550	$5,000	$19,500	($14,500)	$44,050
12	$44,050	$0	$21,700	($21,700)	$22,350
13	$22,350	$19,000	$1,500	$17,500	$39,850
Total	$39,000	$153,000	$152,150	$850	$39,850

The arithmetic for the weeks that matter:

Week 11: $58,550 + $5,000 – $19,500 ($14,000 tax distribution + $4,000 card payment + $1,500 contractors) = $44,050
Week 12: $44,050 + $0 – $21,700 ($13,000 payroll + $7,200 insurance + $1,500 contractors) = $22,350
Week 13: $22,350 + $19,000 ($14,000 late invoice + $5,000 project) – $1,500 = $39,850
Quarter check: $39,000 + $153,000 – $152,150 = $39,850

The low point is $22,350 at the end of week 12, which is $7,650 below the $30,000 floor, in a quarter that finishes $850 ahead.

Built at the start of week 1, the forecast shows this eleven weeks early. If the late client pays one week sooner, week 12 ends at $36,350. Paying the tax distribution earlier, in week 9, does nothing for week 12, because the balance is cumulative. Only pulling cash in before week 12, or pushing a payment past it, moves the low point.

13-Week Forecast vs Monthly Forecast vs Budget

A budget sets targets and tells you whether you are on track. It does not tell you when cash arrives.

A 12-month forecast runs monthly and is the right tool for hiring, pricing, and financing decisions. It is too coarse to catch one bad week. In the example, month-end cash is $47,850, $45,700, and $39,850, all above the floor. The $22,350 week never shows up.

The 13-week forecast is the operating tool you update weekly.

As for the floor, anyone who quotes one universal number is guessing. It depends on payroll frequency, customer concentration, and how lumpy your receipts are. Drafted retainers and an open credit line let you run leaner. Two clients supplying most of your receipts means you need more. In the example, $30,000 is about two and a half weeks of average disbursements ($152,150 divided by 13 is roughly $11,700 a week).

6 Mistakes That Wreck a 13-Week Forecast

Starting from a balance nobody reconciled. If week one’s beginning cash is wrong, all thirteen ending balances are wrong. Fix: start from the bank, subtract uncleared payments, and catch up the books if they lag (our post on bookkeeping mistakes covers the usual culprits).
Spreading monthly bills evenly across weeks. Dividing rent by four hides the week when rent, software, and payroll stack up. Fix: put each payment in the week it actually clears.
Forecasting card purchases instead of the card payment. Cash leaves when you pay the statement, not when you swipe. Fix: forecast the statement payment only.
Including non-cash expenses. Depreciation and accruals do not move money. Fix: if it will not appear on the bank statement, leave it out.
Forgetting the owner’s taxes. The IRS says sole proprietors, partners, and S corporation shareholders generally have to make estimated tax payments if they expect to owe $1,000 or more, and it splits the year into four payment periods, each with its own due date. Fix: if the business funds those payments, give each one its own line.
Never checking last week’s forecast against what happened. Rolling the forecast forward is not the same as testing it. Fix: each week, record forecast versus actual and note why any large line missed.

Your 13-Week Cash Flow Forecast Checklist

Pull today’s bank balance and subtract every payment that has not cleared.
List every open invoice in the week you realistically expect payment, based on that customer’s history.
Place each recurring payment in the week it clears: payroll, rent, software, loans, card payments.
Scan the next 13 weeks for irregular items: tax payments, insurance renewals, annual subscriptions, distributions.
Set a minimum cash floor and highlight every week below it.
For each highlighted week, write one action and the date you will take it.
Block 30 minutes at the same time every week to roll the forecast forward and compare last week to actual.

Get a 13-Week Forecast That Actually Gets Used

For a head start, our spreadsheet templates include the Cash Flow Forecasting Tool, which has a 13-week detailed cash flow alongside a 12-month rolling forecast and best and worst case scenarios.

If you would rather have it built around your actual accounts, with someone beside you for the first few weekly updates, that is the work we do as a fractional CFO. Book a free 20-minute consultation and bring your bank balance and open invoices.

A shortfall you see eleven weeks out is a scheduling problem. One you find on payday is an emergency.

Simply Spreadsheets helps real estate investors and small business owners make confident decisions with clean, reliable numbers. Founded by Erin Onsager, a fractional CFO with more than 20 years of finance experience, the firm builds custom spreadsheets, financial models, and analysis that turn raw data into clear answers.