How to Build a 90-Day Cash Flow Forecast

How to Build a 90-Day Cash Flow Forecast

A cash flow forecast is not accounting. It is a simple prediction of the money in your bank account each week for the next quarter, and it is the single most useful spreadsheet a small business owner can maintain.

Why 90 days, weekly

Monthly forecasts hide the problem. Most businesses can be comfortably cash-positive for a month while being unable to make payroll in week three. Weekly buckets show the trough. Ninety days is long enough to act — to chase receivables, delay an order, or arrange finance — and short enough to be predictable.

Set up the sheet

One column per week for 13 weeks. Rows in four blocks:

1. Opening balance — actual bank balance at the start of week one.

2. Cash in

• Sales collected in cash or card (settled, not gross)
• Invoice payments expected, dated by when you realistically expect them
• Other income: refunds, grants, loans, owner contributions

3. Cash out

• Supplier payments (dated by terms, not by order date)
• Payroll and contractor payments
• Rent, utilities, insurance
• Loan and finance repayments
• Tax payments — the most commonly forgotten line
• Software, subscriptions, marketing
• Card processing fees

4. Closing balance — opening + in − out. This becomes next week's opening.

Forecast receipts, not invoices

The most frequent mistake is entering invoices on their due date. Enter them on the date the customer actually pays. If a customer with net 30 terms has paid on day 44 for eight quarters running, forecast day 44. Your own history is better data than the terms you agreed.

For card and cash sales, use your settled-funds date, and forecast volumes from last year's same week adjusted for growth — not a flat average, because seasonality is exactly what you are trying to see.

Include the timing nobody remembers

• Quarterly or annual tax payments
• Annual insurance renewals
• Software renewing annually on a random date
• Seasonal inventory buys, which land weeks before the sales they generate
• Holiday payroll timing shifts

These lumpy items are what turn a comfortable forecast into a crisis week.

Read the output

Look for three things:

1. The trough — the lowest closing balance in the 13 weeks, and which week it falls in.
2. The buffer — how far the trough sits above zero. A common target is at least one month of fixed costs.
3. The trend — whether closing balances are drifting up or down across the quarter.

If the trough is below your buffer, you have weeks of notice to fix it. That notice is the entire value of the exercise.

Fixing a shortfall, in order of preference

1. Accelerate receivables. Call the three oldest overdue invoices today. Offer a small early-payment discount on the largest.
2. Delay non-critical outflows. Push a discretionary purchase past the trough week.
3. Negotiate supplier terms. Ask for net 45 on the next order rather than skipping a payment silently.
4. Trim inventory buying. Order narrower and more frequently through the tight weeks.
5. Arrange finance before you need it. A facility negotiated from strength is far cheaper than one negotiated in week 12.

Never solve a cash crunch by silently missing a supplier payment. One phone call in advance preserves a relationship that a missed payment damages for years.

Keep it honest

• Update it every Monday with actual figures for the week that just ended.
• Compare forecast versus actual and note why they differed. After six weeks your estimates get noticeably better.
• Be pessimistic on receipts and realistic on payments. Optimistic forecasts feel better and help nobody.

Make it fast

Our cash flow forecast calculator gives you a running weekly projection in the browser with no signup, and ExpressBizTools shows exactly which invoices are outstanding and how old each one is — the hardest input to gather by hand. Fifteen minutes every Monday is enough to keep a live view of the next quarter.