How to Build a 13-Week Cash-Flow Forecast for Your Business

Why forecast 13 weeks at a time?

A monthly budget can hide a timing problem.

The month may show $70,000 coming in and $65,000 going out. But if payroll is due in week two and the largest customer pays in week four, the business can still run short.

Thirteen weeks is long enough to see several payroll cycles, rent, taxes, customer collections, vendor payments, and near-term spending decisions. It is also short enough to update as facts change.

Use the forecast to answer one question:

Will enough available cash be there when the business needs it?

Start with available cash

Available cash is the money the business can actually use at the beginning of the forecast.

Start with the current bank balance, then subtract money that is already committed to payroll, taxes, customer work, approved vendor payments, debt, or other near-term obligations.

Do not count the same dollar twice. A customer deposit that must pay for materials is not also available for rent. Money set aside for payroll should not be treated as spare cash for a new purchase.

Use the amount left as the starting cash for week one.

Getting this number right matters because an overstated starting balance makes every later week look safer than it really is.

Put collections in the week they are likely to arrive

Forecast cash collections, not sales.

A completed job, signed quote, invoice, or verbal promise does not become available cash until payment clears.

Separate expected receipts into three groups:

• High confidence: card settlements, approved deposits, or confirmed customer payments.
• Expected but exposed: valid invoices that are likely to pay, but whose timing could move.
• Possible: unaccepted quotes, disputed invoices, or work that has not been confirmed.

Optimism belongs in the sales plan. The cash forecast should show what happens when payment timing is less certain.

Put payments in the week they must leave

Use payroll schedules, bank history, contracts, vendor statements, tax dates, rent, debt schedules, and known purchasing plans.

Include:

• payroll and payroll-related payments;
• subcontractors;
• materials, inventory, freight, and suppliers;
• rent, utilities, insurance, vehicles, and software;
• credit cards, loans, and leases;
• tax payments or set-asides;
• owner pay;
• equipment, repairs, marketing, and known one-time purchases.

That does not make the second group unimportant. It shows which decisions are still available before cash becomes urgent.

Roll the balance forward each week

Use the same calculation for every week:

Ending cash = starting cash + cash in − cash out

The ending cash from one week becomes the starting cash for the next.

A four-week example shows how the timing becomes visible.

The month ends with $11,000, but week two is the real decision point because available cash falls to $4,000. If the expected $8,000 collection arrives one week late, week two becomes negative unless the owner changes something. A monthly total would hide that risk.

Find the lowest-cash week and its cause

Do not focus only on the final balance. Mark the lowest projected week and ask why it happens.

The cause may be:

• a customer paying after payroll;
• materials being purchased before a deposit arrives;
• several large payments landing together;
• a growth expense starting before its payback;
• owner pay or another withdrawal occurring at the wrong time;
• work that does not leave enough margin;
• a forecast that depends on uncertain sales.

The purpose is not to imagine every possible disaster. It is to test the assumption most likely to change the low point.

Make one decision before the low week arrives

The forecast matters only when it changes what you do.

Depending on the cause, the next move may be to:

• send completed invoices sooner;
• confirm a customer’s payment date;
• revise deposits or progress billing on future work;
• move a noncritical purchase;
• phase a hiring or growth expense;
• adjust purchasing timing;
• review whether a job leaves enough behind.

Before you spend more or borrow, make sure the response matches the reason cash is falling.

Update the forecast every week

Choose one consistent day.

• Replace the completed week’s estimates with actual cash received and paid.
• Update future collection and payment dates.
• Remove amounts that are no longer likely.
• Add a new thirteenth week.
• Recalculate the lowest-cash week.

Over time, the forecast will show which customers pay late, which costs are routinely forgotten, and which assumptions are too optimistic. Use it to make timing decisions. Do not treat it as a replacement for accurate books, tax reporting, or qualified professional advice.

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• What Should I Fix First in My Small Business?