BizCellsHow to build a 13-week cash flow forecast for a small business
A 13-week cash flow forecast shows, week by week for the next three months, how much cash you'll have in the bank. It starts from today's balance, adds the money you expect to come in and subtracts the bills you expect to pay. It's the best early warning a small business has: it shows a cash gap weeks before it happens.
Why profit isn't enough, and why 13 weeks
A business can be profitable on paper and still run out of cash. You invoice $10,000 in March, but if the client pays in May and rent is due on April 1, the profit doesn't help you in April. Your profit and loss statement tells you whether you're making money; the cash flow forecast tells you whether you can pay the bills.
Thirteen weeks is one quarter. It's far enough ahead to act (chase an invoice, delay a purchase, arrange credit) and near enough that your estimates are still realistic. Weeks are better than months because cash problems happen on specific days.
The structure of the forecast
Each column is a week. Each week runs through the same five lines:
| Line | What it contains |
|---|---|
| Opening balance | Week 1: your real bank balance today. Later weeks: last week's closing balance |
| + Cash in | Invoices due to be paid, recurring income, other expected receipts |
| − Cash out | Rent, salaries, suppliers, subscriptions, loan payments, taxes |
| = Net cash flow | Cash in minus cash out |
| Closing balance | Opening balance plus net cash flow |
Build it in Google Sheets
1. Week headers
In B1, enter the Monday of the current week: =TODAY()-WEEKDAY(TODAY(),3). In C1, =B1+7, and drag across to column N. That gives you 13 week-start dates that roll forward on their own.
2. Cash in from open invoices
If you keep an invoices tab with the amount in column F, the due date in column E and the paid date in column H, the money expected in a given week is:
=SUMIFS(Invoices!$F:$F,
Invoices!$E:$E, ">="&B$1,
Invoices!$E:$E, "<"&B$1+7,
Invoices!$H:$H, "")The last condition only counts invoices that haven't been paid yet. Overdue invoices (due before this week and still unpaid) deserve their own line in week 1, so they don't silently disappear.
3. Recurring items
Make a small table of recurring items: name, amount, frequency (weekly or monthly) and day of the month. For a monthly bill paid on day 1, it lands in the week that contains the 1st. A simple check per week is:
=IF(OR(DAY(B$1)=1, DAY(B$1+6) < DAY(B$1)), amount, 0)That returns the amount when the week starts on the 1st or crosses into a new month. Write one line for each big recurring cost: rent, payroll, software, loan repayments.
4. Totals and balances
- Cash in and cash out:
=SUM()of their lines in each column. - Net cash flow: cash in minus cash out.
- Opening balance: in B, your real balance typed in; in C,
=B[closing row]. - Closing balance: opening balance plus net cash flow.
5. Warnings
Two formulas turn the forecast into an alarm:
- Lowest point:
=MIN(B20:N20)on the closing balance row. - Warning:
=IF(MIN(B20:N20)<0, "Cash goes negative in week of "&TEXT(INDEX(B1:N1, MATCH(TRUE, INDEX(B20:N20<0,0), 0)), "mmm d"), "Cash stays positive")
Add a line chart of the closing balance and conditional formatting that turns negative weeks red.
How to read it every week
- Update week 1's opening balance with your real bank balance.
- Mark invoices that were paid and add any new ones.
- Look at the lowest point. If it's below your safety cushion (many businesses aim for at least one month of fixed costs), act now: chase invoices, move a purchase, or talk to your bank.
Common mistakes
- Assuming clients pay on the due date. Use the date they usually pay. If a client is always two weeks late, forecast it that way.
- Forgetting annual and quarterly bills: insurance, software renewals, tax payments.
- Never updating the opening balance. After a few weeks the forecast drifts away from reality.
- Forecasting income as hoped rather than expected. Only count sales that are invoiced or very likely.
Skip the formulas
Business Manager includes a rolling 13-week cash flow tab built from today's cash, open invoices and recurring items, with the lowest point and a warning if cash goes negative. It's a Google Sheets template, ready in minutes.
See the template · $19 one-timeFAQ
What's the difference between a cash flow forecast and a cash flow statement?
A cash flow statement reports what already happened. A forecast estimates what will happen. Small businesses usually get more value from the forecast.
How often should I update it?
Once a week, ideally the same day. It takes 10 to 15 minutes once it's set up.
Do I need a 13-week forecast if I'm a freelancer?
If your income is irregular, yes. It's the easiest way to know whether a quiet month is a problem or not.