How do I create a cash flow forecast for my small business?

A cash flow forecast projects your expected cash inflows and outflows over a future period — typically 13 weeks or 12 months — so you can spot shortfalls before they happen and plan accordingly. Build it from your actual sales history, known expense schedules, and realistic collection timing.

A cash flow forecast tells you when your bank account will be tight — before it happens. Unlike a profit and loss statement, which shows whether you're profitable on paper, a forecast shows whether cash will actually be in your account when bills are due. The SBA recommends that every small business owner maintain a rolling short-term cash forecast.

Choose your format: 13-week or 12-month

13-week (rolling quarterly): best for operational decisions — shows week-by-week cash position 90 days out. Update weekly. Most useful for businesses with variable revenue or tight margins.
12-month (annual): best for strategic planning — annual budget, loan projections, hiring decisions. Update monthly. Less granular but shows seasonal patterns clearly.
Many businesses maintain both: a 13-week rolling forecast for near-term management and an annual plan for goal-setting.

Step 1: Project cash inflows

Start with your actual sales history from the past 12 months. For each future week or month, estimate: expected invoices you'll collect (based on your average collection lag from the profit and loss statement), any known upfront payments or retainers, and other income (interest, asset sales). Be conservative — use 80–85% of expected collections to account for slow-payers and disputes.

Step 2: Project cash outflows

Fixed obligations: rent/lease, loan payments, insurance premiums, payroll (salaried staff). These are known and date-specific — enter them exactly.
Variable expenses: inventory, contractor labor, commissions, utilities. Estimate from historical averages; adjust for seasonal patterns.
One-time and irregular items: tax deposits, equipment purchases, annual license renewals. Pull from your tax calendar and expense history.
Don't forget quarterly estimated tax payments — see IRS Form 1040-ES for the due date schedule.

Step 3: Calculate the running cash balance

For each period: Opening Balance + Cash In - Cash Out = Closing Balance. The closing balance of one period is the opening balance of the next. Any period where the closing balance goes negative is a shortfall that needs a fix — before it happens. Common fixes: delay a discretionary purchase, accelerate collections on outstanding invoices, or draw on a business line of credit. The SBA's SCORE mentors offer free cash flow forecasting templates and guidance.

Step 4: Update it regularly

A forecast you built once and never updated is a historical document, not a planning tool. Replace estimates with actuals each week (or month). Compare projected vs. actual — the variance reveals systematic errors in your assumptions (e.g., you consistently overestimate collection speed). Over time, your forecast accuracy improves and becomes genuinely useful for decisions.

What the SBA and IRS say

The SBA identifies cash flow forecasting as a foundational practice for small-business financial management and recommends that owners review and update projections regularly. — SBA — Manage your finances
The IRS requires most self-employed individuals and small businesses to make quarterly estimated tax payments; failure to do so can result in underpayment penalties. — IRS — Form 1040-ES
SCORE, the SBA's largest network of volunteer business mentors, provides free cash flow forecast templates and one-on-one mentoring to help small businesses project and manage liquidity. — SBA / SCORE

Key takeaways

A cash flow forecast projects when cash will be in your account — not just when revenue is earned.
Start with a 13-week rolling forecast for near-term management; add a 12-month annual plan for strategy.
Use actual sales history and be conservative on collection timing — 80–85% of expected receipts.
Any week showing a negative closing balance is a problem to solve now, not later.
Update actuals weekly and compare to your forecast — variance analysis is how you get better at projecting.