13-Week Cash Flow Forecast: How to Build One (With Example)

A 13-week cash flow forecast is one of the most useful tools a finance team can maintain. It shows when cash will be tight, which commitments are coming, and whether the business can absorb a late payment or an unexpected cost.

It is also easy to build badly. A forecast that is updated once a month, mixes planned and actual movements, or ignores bank timing gives false confidence.

This guide shows a practical direct-method forecast you can maintain in under 30 minutes a week.

Why 13 weeks?

Thirteen weeks is roughly one quarter:

Long enough to cover payroll cycles, rent, quarterly taxes and supplier terms.
Short enough to use real invoices and commitments instead of vague annual assumptions.
Short enough to update weekly without rebuilding the model.

For most small and mid-sized businesses, a 13-week forecast is more actionable than a 12-month budget. Use the annual plan for direction and the 13-week forecast for decisions.

Use the direct method

There are two common approaches:

Direct method: forecast actual receipts and payments by week.
Indirect method: start with profit and adjust for working-capital changes.

For a 13-week horizon, use the direct method. You care about when money hits the bank, not when revenue is recognized.

Step 1: Set the opening cash position

Start with the current cleared balance for each bank account, not the accounting-system cash balance. Include:

Operating accounts
Savings or reserve accounts you can access
Restricted cash you cannot use
Credit lines only if they are confirmed and available

If the opening balance is wrong, every week after it is wrong.

Step 2: List expected receipts by week

Group receipts by reliability:

Committed: signed contracts or issued invoices with a known due date.
Likely: recurring customers with a predictable payment pattern.
Possible: pipeline or overdue invoices with collection risk.

For each item, record the customer, invoice, amount, expected week and confidence. Do not spread annual revenue evenly across the quarter. Use actual invoices and payment terms.

Step 3: List expected payments by week

Include every material outflow:

Payroll and contractor payments
Rent and utilities
Supplier and vendor payments
Taxes and social contributions
Loan repayments and interest
Subscriptions and software
One-off purchases and professional fees

Separate fixed costs from variable costs. Fixed costs define the minimum cash requirement; variable costs are where you have flexibility.

Step 4: Add the weekly roll-forward

The math is simple:

Closing cash = opening cash + receipts − payments

Do it for all 13 weeks and track the lowest point. That low point is the number that matters. A business can be profitable on paper and still fail if the low point is below zero before receivables arrive.

Example structure

Week	Opening	Receipts	Payments	Closing
1	80,000	18,000	22,000	76,000
2	76,000	12,000	31,000	57,000
3	57,000	25,000	19,000	63,000
4	63,000	8,000	48,000	23,000

The closing balance is not the only output. The shape of the curve tells you when to collect faster, delay a discretionary payment, or arrange a credit line before you need it.

Step 5: Add scenarios

Maintain at least three versions:

Base case: the most likely timing.
Downside: key receipts slip by two to four weeks.
Upside: collections improve or a large deal closes early.

The downside case is the one to review with leadership. It answers the real question: “If our two largest customers pay late, what happens to payroll?”

Step 6: Update weekly and compare

A forecast becomes useful when it is compared with reality.

Each week:

Replace forecast weeks with actual bank movements.
Roll the horizon forward by one week.
Record the variance and its cause.
Update the next four weeks based on new information.

Track forecast accuracy over four weeks. If the forecast is consistently optimistic, the problem is usually receipt timing, not the spreadsheet formula.

Common mistakes

Using accrued revenue instead of bank receipts. Revenue is not cash.
Ignoring payment terms. A 30-day invoice is not cash today.
Mixing planned and executed movements. You lose the ability to explain variance.
Forecasting only the closing balance. The low point and timing matter more.
Updating monthly. A 13-week forecast is a weekly operating tool.
Hiding unplanned payments. If it is not visible, it cannot be managed.

How Spifex helps

Spifex keeps the forecast connected to execution:

Planned entries with dates, owners and categories
Settlements and partial settlements against bank accounts
Continuous reconciliation with planned-versus-actual variance
KPIs for accuracy, unplanned movements and reconciliation lag

Explore Cashflow or read the cash flow management guide for small businesses.

Next step

Build the first version with your next 13 weeks of known receipts and payments. Then add one rule: no payment is executed without a planned entry or an explicit “unplanned” label.

Start free with Spifex and keep the forecast, settlements and reconciliation in one workspace.