13-Week Cash Flow Forecast Tool — Free, Online
Project your cash position across 13 weeks to see the week it turns negative. Opening balance plus average weekly inflow and outflow.
13-Week Cash Flow Forecast
End of week 13 balance
$35,000
Lowest weekly balance
$35,000
Net weekly delta
$-5,000
| Wk | Inflow | Outflow | Bal |
|---|---|---|---|
| 1 | $25,000 | −$30,000 | $95,000 |
| 2 | $25,000 | −$30,000 | $90,000 |
| 3 | $25,000 | −$30,000 | $85,000 |
| 4 | $25,000 | −$30,000 | $80,000 |
| 5 | $25,000 | −$30,000 | $75,000 |
| 6 | $25,000 | −$30,000 | $70,000 |
| 7 | $25,000 | −$30,000 | $65,000 |
| 8 | $25,000 | −$30,000 | $60,000 |
| 9 | $25,000 | −$30,000 | $55,000 |
| 10 | $25,000 | −$30,000 | $50,000 |
| 11 | $25,000 | −$30,000 | $45,000 |
| 12 | $25,000 | −$30,000 | $40,000 |
| 13 | $25,000 | −$30,000 | $35,000 |
13 weeks (~one quarter) is the standard horizon for short-term cash planning. If any week dips negative, you need to bring in receivables earlier, delay payables, or arrange a short-term credit facility.
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Cash runs out before profit catches up
Most businesses fail not because they are unprofitable but because they run out of cash. A business showing 10% net margins on the profit-and-loss statement can be insolvent within weeks if customers pay on 60-day terms while suppliers demand payment in 10. That gap is invisible to accounting — profit is accrual, cash is actual.
Thirteen weeks is the right horizon
A quarter is long enough to see a problem coming with time to act, and short enough that the numbers are still knowable rather than guessed. Take a business opening with $50,000, bringing in $25,000 a week and spending $30,000: it loses $5,000 a week and crosses into negative cash in week 11 — comfortably inside the window, with roughly two months of warning to accelerate collections, renegotiate payment terms or arrange a facility.
What this tool calculates
The forecast takes your opening balance, average weekly inflow and average weekly outflow, then projects the balance forward week by week across all thirteen weeks. It surfaces the lowest point you reach and flags the week it turns negative, so you can see which week is critical and how large the shortfall is.
What it does not model
The forecast assumes the same inflow and outflow every week. It will not catch a seasonal November surge, a one-off equipment purchase, or a customer who pays 90 days late. More importantly it treats inflow as cash arriving, not as invoices issued — if your invoices convert to cash 45 days later, the forecast is 45 days optimistic. Pair it with the Accounts Receivable Aging Analysis to see how much of that inflow is still sitting in receivables, or the DSO & DPO Calculator to measure the gap between getting paid and paying out.
How to use the 13-Week Cash Flow Forecast
Takes about a minute. No signup, no download, your data stays in your browser.
- 1Open the tool. Scroll up to the 13-Week Cash Flow Forecast above — it loads instantly in your browser, no install needed.
- 2Enter your values. The fields come pre-filled with realistic defaults so you can see how it works — replace them with your own numbers.
- 3Read the result. The output updates instantly. Copy or share it — nothing is uploaded to a server, everything stays on your device.
Frequently asked questions
Common questions about the 13-Week Cash Flow Forecast.
Why 13 weeks specifically?
Thirteen weeks is one quarter — long enough to see a cash problem far enough ahead to do something about it, but short enough that the inflow and outflow figures are still based on known commitments rather than guesses. It also lines up with the quarterly cycle most reporting and lending arrangements already use.
My forecast turns negative in week 7. What does that mean?
It means your average outflow exceeds your average inflow and the opening balance runs out at that point. The tool is a diagnostic, not advice: it tells you when, not what to do. The usual levers are collecting faster, paying later, cutting discretionary spend, or arranging finance ahead of the shortfall.
I run a seasonal business. Can I forecast quarterly spikes?
Not directly — the tool assumes constant weekly flows. If your sales spike in one month and collapse in another, run it separately for each block using that block's weekly average, or move to a spreadsheet for week-by-week variation. For a seasonal business the constant-flow assumption is usually optimistic.
What is the difference between this forecast and a profit and loss?
A profit and loss shows revenue minus expenses; this shows cash in minus cash out. A business can be profitable on paper and still run dry, because revenue is recorded when invoiced while cash arrives when paid. That timing gap never appears on the P&L and is exactly what this forecast exposes.
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