A 13-week cash flow forecast is a weekly projection of every dollar entering and leaving your bank account over the next quarter, built from actual expected receipts and payments rather than from your P&L. It is the single most useful financial document a founder can maintain, and most companies only build one when a lender, an investor, or a near-miss on payroll forces them to.
It answers one question your accounting system cannot: on which specific week does cash get tight?
This guide covers what the forecast is, why the window is 13 weeks, how to build one line by line, a worked example you can copy, and the five mistakes that make most 13-week models useless within a month.
What is a 13-week cash flow forecast?
A 13-week cash flow forecast projects your cash position week by week for one quarter ahead. Each week shows an opening balance, cash in, cash out, and a closing balance that becomes the next week's opening.
The critical distinction: it is built on the direct method. You forecast actual cash movements — this invoice collects in week 4, payroll runs in weeks 2, 4, 6 — rather than starting from net income and adjusting for non-cash items.
That distinction is why the tool works. Your income statement can show a profitable month while your bank account empties, because revenue is recognized when earned and cash arrives when customers decide to pay. A 13-week forecast ignores accounting and tracks money.
Why 13 weeks and not 12 or 26?
Thirteen weeks is exactly one quarter. That matters for three practical reasons:
It matches how the business already reports. Board packs, investor updates and covenant tests run on quarters. A 13-week window lines up with the cycle everyone is already looking at.
It is long enough to act. Most cash problems have a fix with a four-to-eight week lead time — accelerating collections, delaying a hire, drawing on a facility, renegotiating payment terms. A four-week forecast tells you about a problem you can no longer solve. Thirteen weeks gives you room.
It is short enough to be accurate. Beyond about a quarter, receipt timing becomes guesswork. The forecast's authority comes from being specific about weeks, and specificity decays fast past week 13.
The format is long-established in restructuring and asset-based lending, which is why it is instantly recognizable to anyone reviewing your finances — a lender or an investor will know exactly what they are looking at.
Direct method vs indirect method
| Direct method | Indirect method | |
|---|---|---|
| Starts from | Expected cash receipts and payments | Net income |
| Answers | When will cash move? | Why did cash differ from profit? |
| Source data | AR aging, AP aging, payroll calendar, contracts | Income statement and balance sheet |
| Used for | Forecasting forward | Reporting the past (statement of cash flows) |
| Update rhythm | Weekly | Monthly or quarterly |
Most companies' statutory cash flow statement uses the indirect method — both IAS 7 and ASC 230 permit either, and indirect is the common choice. Your 13-week forecast should not follow suit. If someone builds you a 13-week model that starts from EBITDA and works down, they have built a reporting document wearing a forecasting costume.
Free 13-week cash flow forecast template
This free Excel template does everything on this page. Enter your bank balance, receipts and payments, and it rolls cash forward week by week, finds your lowest cash week and shows how many weeks of outflows that covers.
Each Monday, enter last week's actuals, and it calculates the variance line by line. The Downside tab shows what happens if collections arrive late: enter a delay under any week's collections and see the new low point.
It comes pre-filled with the worked example below, so you can see how it works before entering your own numbers.
When do founders actually need one?
You do not need a 13-week forecast forever. You need it when the answer to "will we be fine" stops being obvious. In practice, that is:
- Runway under 12 months. Below a year, weekly resolution starts to matter. Below six months it is not optional.
- Lumpy revenue. Enterprise contracts, milestone billing, seasonal demand — anything where a single late payment moves the month.
- You are raising. Investors ask for it, and arriving with one already maintained signals a level of control that changes the conversation.
- You have debt. Lenders with covenants frequently require a rolling 13-week as a condition. Venture debt and asset-based facilities almost always do.
- You just had a scare. If payroll was ever close, build it that week.
Out of the 40 companies I've built financial models for, 80% did not have a working cash forecast when I arrived. Ten of those had built one at some point and stopped updating it within two months.
How to build a 13-week cash flow forecast
Step 1 — Set the structure before you enter a number
Columns are weeks. Use the week-ending date, not "Week 1" — labels drift and dates do not. Thirteen forecast columns, plus a column for each completed week so actuals sit beside the forecast.
Rows group into four blocks:
- Opening cash — one line, per bank account if you hold several
- Cash receipts — money in
- Cash disbursements — money out
- Net movement and closing cash
Keep it to one sheet. The most common failure in a first model is over-engineering — a 40-tab workbook nobody updates is worth less than a one-page forecast someone refreshes every Monday.
Step 2 — Start from the bank balance, never the ledger
Week 1 opening cash is the cleared balance in your bank account this morning. Not the balance in your accounting system, which includes uncleared items and timing differences.
This sounds pedantic. It is the difference between a forecast people trust and one they quietly stop opening.
Step 3 — Map receipts from the AR aging, customer by customer
Do not forecast revenue and assume a collection lag. Take your accounts receivable aging report and place each open invoice in the week you genuinely expect it to land.
| Receipt line | Source | How to time it |
|---|---|---|
| Collections — existing invoices | AR aging | Invoice date + that customer's actual historical payment behavior |
| Collections — new invoices | Sales pipeline × close rate | Expected invoice date + terms + observed slippage |
| Subscription / recurring | Billing system | Renewal dates, net of expected churn |
| Financing inflows | Term sheets, facilities | Only when documented — never "expected" |
| Tax refunds, grants, other | Filings and correspondence | Only with a confirmed date |
The phrase doing the work is actual historical payment behavior. A customer on net-30 terms who has paid on day 52 for six consecutive quarters pays on day 52. Forecasting them at day 30 is not optimism, it is a known error.
When cash forecasting is part of a fully managed finance function, outsourced CFO services can connect this weekly view to reporting and controls.
Step 4 — Map disbursements from the AP aging and the calendar
Disbursements are easier because most are known. Split them into committed and discretionary — this is what lets you model levers later.
Committed (contractual, hard to move quickly):
- Payroll and payroll taxes — use the actual pay calendar, including the months with three pay runs
- Rent and lease payments
- Debt service — principal and interest, on the exact due dates
- Insurance premiums
- Software and infrastructure on annual renewal
Discretionary (movable under pressure):
- Vendor payments from the AP aging
- Marketing spend
- Contractors and agencies
- Travel
- Capital expenditure
Two lines founders routinely omit and then get caught by: quarterly tax payments and annual software renewals. Both are large, both are predictable, and neither appears in a monthly average.
Step 5 — Build the roll-forward
The arithmetic is trivial and the discipline is not:
Closing cash (week N) = Opening cash (week N)
+ Total receipts (week N)
− Total disbursements (week N)
Opening cash (week N+1) = Closing cash (week N)
Every week links to the last. One hardcoded balance in the middle of the roll-forward breaks the model silently, and it will not be obvious which week is wrong.
Step 6 — Add the variance column, which is the whole point
At the end of each week, enter what actually happened next to what you forecast. Compute the variance by line.
| Line | Forecast week 1 | Actual week 1 | Variance | Note |
|---|---|---|---|---|
| Opening cash | 520 | 520 | — | |
| Collections | 145 | 98 | (47) | Northwind slipped to wk 3 |
| Payroll | (82) | (82) | — | |
| Vendors | (34) | (41) | (7) | Unplanned legal invoice |
| Other | (12) | (12) | — | |
| Closing cash | 537 | 483 | (54) |
$000s. Ties to week 1 of the worked example below.
Without this column you have a projection. With it you have a forecast that gets better every week, because you can see which assumptions are systematically wrong. Most models fail here — built once, admired, never reconciled.
Example
A B2B services company: $520,000 in the bank, payroll of $82,000 per run on a biweekly cycle, and three large receivables outstanding.
| Week ending | Opening | Collections | Other in | Payroll | Vendors | Other out | Closing |
|---|---|---|---|---|---|---|---|
| Wk 1 — Sep 6 | 520 | 145 | — | (82) | (34) | (12) | 537 |
| Wk 2 — Sep 13 | 537 | 38 | — | — | (28) | (9) | 538 |
| Wk 3 — Sep 20 | 538 | 92 | — | (82) | (31) | (11) | 506 |
| Wk 4 — Sep 27 | 506 | 61 | — | — | (26) | (48) | 493 |
| Wk 5 — Oct 4 | 493 | 118 | — | (82) | (35) | (10) | 484 |
| Wk 6 — Oct 11 | 484 | 44 | — | — | (29) | (9) | 490 |
| Wk 7 — Oct 18 | 490 | 76 | — | (82) | (33) | (11) | 440 |
| Wk 8 — Oct 25 | 440 | 52 | — | — | (27) | (95) | 370 |
| Wk 9 — Nov 1 | 370 | 134 | — | (82) | (36) | (12) | 374 |
| Wk 10 — Nov 8 | 374 | 41 | — | — | (30) | (9) | 376 |
| Wk 11 — Nov 15 | 376 | 88 | — | (82) | (32) | (11) | 339 |
| Wk 12 — Nov 22 | 339 | 57 | — | — | (28) | (10) | 358 |
| Wk 13 — Nov 29 | 358 | 121 | — | (82) | (34) | (12) | 351 |
$000s. Week 4 'other out' includes a quarterly estimated tax payment; week 8 includes annual insurance and software renewals.
Read the closing row rather than the total. Cash never goes negative, so a monthly view would show no problem at all. But two weeks need attention. Week 8 has the sharpest drop, $70k, when the insurance and software renewals land. Week 11 is the lowest point, $339k, about 3.6 weeks of average outflows ($95k a week). That's the week that needs a decision, and it's invisible in any monthly report.
That is the entire value of the tool. Not the ending balance. The shape.
Downside: what if two big collections arrive late?
The base case assumes every customer pays when expected. Now suppose the two biggest collection weeks, week 1 ($145k) and week 9 ($134k), each arrive three weeks late. Nothing else changes.
| Week ending | Base closing cash | Downside closing cash |
|---|---|---|
| Wk 1 — Sep 6 | 537 | 392 |
| Wk 3 — Sep 20 | 506 | 361 |
| Wk 8 — Oct 25 | 370 | 370 |
| Wk 9 — Nov 1 | 374 | 240 |
| Wk 11 — Nov 15 | 339 | 205 |
| Wk 13 — Nov 29 | 351 | 351 |
$000s. Both payments still arrive within the 13 weeks, so week 13 ends at the same balance.
The lowest point falls from $339k to $205k, still in week 11. That's about 2.2 weeks of average outflows instead of 3.6, caused only by two customers paying late. Week 13 looks the same in both cases, which is why the ending balance alone is never enough.
Run this before you need it. The template's Downside tab does it for your numbers: enter a delay under any week's collections, add a haircut if you want one, and it shows the new lowest week.
The weekly cadence
The forecast is a habit, not a document. The rhythm that works:
Monday morning, 30 minutes.
- Pull the cleared bank balance
- Enter last week's actuals beside the forecast
- Review variances over your materiality threshold — explain each one in a sentence
- Roll the window forward one week, adding a new week 13
- Update receipt timing for anything you learned — a customer confirming a date, an invoice disputed
- Circulate the closing-cash row and the three largest variances
Thirty minutes. The roll-forward is what makes it rolling — you always have a full quarter of visibility rather than a window that shrinks until it is useless.
Five mistakes that break most 13-week models
1. Forecasting revenue instead of collections. The most common and most damaging. Revenue is an accounting event; collection is a cash event. On net-45 terms with typical slippage they are two months apart.
2. Using monthly averages divided by 4.33. Payroll does not run evenly. Rent lands on the 1st. Tax is quarterly. Averaging destroys the timing information that is the only reason to build a weekly model.
3. Forgetting the three-payroll month. A biweekly payroll (every two weeks, 26 runs a year) produces three runs in two months of every year. Founders discover this in the week it happens.
4. Building it once. A model without weekly actuals and variance analysis is a projection, and it decays immediately. The forecast's accuracy comes from reconciliation, not from the initial build.
5. Modeling only the base case. A forecast with one scenario is a best case. Run a downside where your two biggest collection weeks slip by three weeks, as in the example above. That's the scenario you actually need a plan for.
The one I see most
Across the forecasts I review, the most common error isn't in the formulas — it's forecasting collections off invoice terms instead of observed payment behavior. Roughly two-thirds of the models I see put net-30 customers at 30 days when their actual average is closer to 50.
On a company collecting $400k a month, that's a three-week hole in the forecast that stays invisible until the week it isn't. It's also the easiest thing on this page to fix: pull twelve months of payment dates per customer and use the median, not the terms.
How the 13-week fits with your other financial tools
| Tool | Horizon | Granularity | Question it answers |
|---|---|---|---|
| 13-week cash flow | 1 quarter | Weekly | When does cash get tight? |
| Annual budget | 1 year | Monthly | What are we committing to spend? |
| 3-statement model | 3–5 years | Monthly / quarterly | Is the business model viable? |
| Statement of cash flows | Historic | Monthly | Why did cash differ from profit? |
These are complements, not alternatives. The 13-week is the only one operating at the resolution where payroll decisions are actually made.
Frequently asked questions
Clear answers to the questions founders ask most often.
A weekly projection of cash receipts and disbursements over one quarter, built using the direct method from actual expected payment timing rather than from the income statement. It shows the specific week cash gets tight.
Thirteen weeks is one quarter, which aligns with board and covenant reporting. It is long enough that you can still act on a problem it surfaces, and short enough that weekly receipt timing remains credible.
The statement of cash flows is a historic accounting report built on the indirect method, starting from net income. A 13-week forecast is forward-looking and built on the direct method, starting from expected cash movements. Different direction, different method, different purpose.
In practice, weeks 1–4 tighten considerably once the weekly reconciliation habit is established, weeks 5–8 drift wider, and weeks 9–13 should be treated as directional rather than precise. If week 2 is materially wrong, the problem is usually receipt timing assumptions rather than the model.
Companies with under 12 months of runway, lumpy or contract-based revenue, active debt covenants, or an imminent raise. Lenders frequently require one as a condition of facilities.
Direct, always, for a forecast. The indirect method reconciles profit to cash for reporting; it cannot tell you which week a payment lands.
Weekly, without exception. The variance analysis is where the value lives — a model updated monthly is a projection, not a forecast.
Yes, and you should. It is one sheet, thirteen columns and roughly thirty rows. Dedicated tools help at scale, but the discipline matters far more than the software.
Collections against existing invoices from your AR aging, expected collections on new invoices, recurring or subscription billings, and any documented financing inflows. Time each by observed customer payment behavior, not by stated terms.
One where you add a new week 13 each time a week completes, so you always hold a full quarter of visibility. The alternative — a fixed window that shrinks — becomes useless around week 9.
Yes. ControlFi's free Excel template on this page includes a forecast tab, an actuals and variance tab, and a downside tab for late collections. It comes pre-filled with the worked example, so you can see how it works before entering your own numbers.
Building one properly
The mechanics on this page are simple. What makes a 13-week forecast valuable is the weekly discipline behind it: the reconciliation, the variance explanations and honest receipt timing.
ControlFi builds and maintains rolling cash forecasts as part of its fractional CFO services, alongside the 3-statement model behind them.