Many profitable small businesses run out of cash because the money arrives later than the bills. A cash flow forecast does not predict the future perfectly; it shows you where the gap is and gives you time to act.
This guide builds a 13-week rolling forecast in a spreadsheet. It covers the categories, the update routine and the early warnings that matter more than the final balance.
Key facts
- Forecast weekly for the next 13 weeks.
- Include tax, loan repayments and owner drawings.
- Use realistic collection dates, not invoice dates.
- Update actuals every week and re-forecast the rest.
Why 13 weeks
Thirteen weeks is long enough to see a quarterly tax bill or a seasonal dip, and short enough to forecast with reasonable accuracy. Annual budgets hide the timing problem; a monthly view is too coarse for payroll and supplier runs.
A weekly forecast forces you to think about when money actually moves. It also gives lenders and advisers a credible document if you need a facility. Banks are far more receptive to a forecast that shows a specific gap than to a general request for cash.
Set up the categories once
Start with opening cash, then cash in and cash out. Cash in includes customer receipts, deposits, grants, loan drawdowns and tax refunds. Cash out includes payroll, rent, suppliers, tax, loan repayments, insurance, software and owner drawings.
Keep the categories stable from week to week so you can compare actuals with forecast. Add a line for one-off items rather than forcing them into a regular category. The forecast should be readable by someone who does not know your bookkeeping system.
Use collection dates, not invoice dates
The biggest error in a cash forecast is treating an issued invoice as cash. If customers pay in 45 days, the money belongs in week seven, not week one. Use your actual collection history by customer segment.
For late payers, apply a realistic delay and a small bad-debt allowance. If a customer has missed two promises, do not forecast payment on the third. A forecast that assumes best behaviour is a wish, not a tool.
Include the bills that arrive quarterly
Tax, insurance, software renewals and loan repayments are easy to forget because they do not appear every week. List every known bill for the next twelve months with its due date, then slot it into the correct forecast week.
Add payroll taxes and pension contributions at the same time as payroll. A 13-week window will usually contain at least one quarterly obligation. If the forecast only looks comfortable because that bill is missing, it is not comfortable.
A cash forecast does not stop bad news. It stops the bad news from arriving as a surprise.
Update weekly in ten minutes
Each week, replace the forecast for the week just ended with the actual bank movement. Then re-forecast the remaining twelve weeks. The rolling update keeps the tool honest and stops it becoming a historical document.
Assign one person to own it and review it at the same time each week. The review should ask three questions: what changed, why, and what action is needed this week. A forecast nobody reads is an expensive spreadsheet.
Spot the gap before it becomes a crisis
Watch the lowest cumulative cash balance, not the closing balance of each week. A single bad week can be covered; a sustained negative trend cannot. Mark the week the balance falls below your minimum buffer.
Act early: chase receivables, delay discretionary spending, negotiate supplier terms, use a credit facility or reduce owner drawings. The earlier you act, the more options you have. Our business emergency fund guide explains how much buffer to hold.
Turn the forecast into a habit
Link the forecast to your bookkeeping so actual cash is easy to import. Keep a simple dashboard with cash balance, weekly burn, receivables due and the lowest projected point. Review it before you commit to a new hire or a large purchase.
After three months, compare forecasts with actuals and adjust your assumptions. The aim is not a perfect prediction but a reliable early warning system. That is what keeps a growing business solvent while it waits for profit to catch up.
Official source: sba.gov.
