How a 13-Week Cash Flow Forecast Finds the Lowest Week

A 13-week cash flow forecast lists the cash a company expects to receive and pay in each of the next 13 weeks and carries the balance forward, so the lowest week shows. Insolvency law, lenders and the payroll all test that week. Month-end figures can hide it, which is why the forecast runs weekly.

Four questions follow: why weekly, how to date the receipts, why 13 weeks, and why a company nowhere near distress should bother.

How the 13-week forecast differs from the two documents it is confused with

	13-week cash flow forecast	Monthly runway model	Annual budget
Question	Can the company pay what falls due in each week?	How many months until the cash runs out?	What does the company plan to earn and spend?
Time step	Week	Month	Month or quarter
Horizon	13 weeks, rolled forward every week	Until the cash runs out	The fiscal year
Method	Direct: each receipt and payment on its expected date	Usually indirect, from the profit and loss	Accrual profit and loss
Decision number	Lowest weekly closing balance	Months of runway	Variance against plan
Who tests it	Lenders in a workout, for example against a 15% permitted variance every other week	Investors and boards	Boards

Source: CX Cash synthesis; lender practice from Accelerate Diagnostics’ 2025 DIP term sheet.

Closing cash = opening cash + receipts − payments, each week; the decision number is the lowest of the 13 closing balances

A 13-week cash flow forecast runs the cash-flow test of insolvency forward

UK law has two tests for a company that cannot pay its debts. Section 123 of the Insolvency Act 1986 deems a company unable to pay “if it is proved to the satisfaction of the court that the company is unable to pay its debts as they fall due”. A second limb applies when its assets are worth less than its liabilities (Insolvency Act 1986, s. 123). The UK Supreme Court notes their usual names: cash-flow and balance-sheet insolvency. Under the US Uniform Commercial Code, being “unable to pay debts as they become due” is one of the three meanings of insolvent (UCC § 1-201).

How far ahead does the cash-flow test look? The Supreme Court answered in 2013, in BNY Corporate Trustee Services v Eurosail. Lord Walker held that the test covers “debts falling due from time to time in the reasonably near future”, whose length “will depend on all the circumstances, but especially on the nature of the company’s business”. Beyond that horizon, “any attempt to apply a cash-flow test will become completely speculative” (Eurosail [2013] UKSC 28, para 37). A 13-week forecast is one practical reading of that near future: far enough ahead to see the debts coming, near enough to put a date on each one.

German law puts numbers on the same idea. A debtor is illiquid when it cannot meet payment obligations that are due, and the directors of a company must file for insolvency no later than three weeks after that point, on pain of up to three years in prison (InsO §§ 17, 15a; our translation). Germany’s Federal Court of Justice separates illiquidity from a mere Zahlungsstockung, a payment stoppage: a shortage of cash that can be closed within three weeks at most (our translation of a 2013 decision, as quoted by German Wikipedia). A board that cannot see three weeks ahead cannot tell which of the two it faces.

Solvency rules and the horizon each one looks across

Rule	What it tests	Horizon
German case law on Zahlungsstockung	Whether a cash shortfall is only temporary	3 weeks to close it
German InsO § 15a	Deadline to file once illiquid	3 weeks
DIP term sheets (Accelerate Diagnostics, Li-Cycle, 2025)	Actual cash against the approved budget	13 weeks, tested every 1 or 2 weeks
UK Insolvency Act s. 123(1)(e), read with Eurosail	Paying debts as they fall due	The reasonably near future
US GAAP going concern (ASU 2014-15)	Meeting obligations as they become due	1 year from issuing the accounts
German InsO § 19	Over-indebtedness, unless survival is likely	12 months
German InsO § 18	Impending illiquidity	24 months, as a rule

Sources: InsO §§ 15a, 18, 19 (our translations); German Wikipedia; Eurosail [2013] UKSC 28; FASB ASU 2014-15; SEC-filed DIP term sheets.

FASB’s going-concern test looks a full year past the date the accounts are issued (FASB, 2014); a 13-week forecast answers the first quarter of that year with dates instead of estimates.

A UK director who “knew or ought to have concluded” that insolvent liquidation could not be avoided can be ordered to contribute to the company’s assets, unless they took every step to minimise the creditors’ potential loss. The yardstick is a reasonably diligent director, and the section reaches shadow directors (Insolvency Act 1986, s. 214). In the US, the IRS can assess unpaid payroll withholding against the individuals responsible, at a penalty “equal to the unpaid balance of the trust fund tax”. It treats paying other creditors while those taxes go unpaid as an indication of willfulness (IRS). For a founder, a short week can become a personal liability as well as a company one.

Weekly is the slowest time step that can see a fortnightly payroll

The law dates each debt, but a monthly model looks at cash once a month, and the largest outflow runs on a shorter cycle. Payroll-related costs make up 76% of a venture-backed startup’s operating expenses in Kruze Consulting’s client data (Kruze Consulting). Monthly pay is the least common schedule. In the Bureau of Labor Statistics’ February 2023 snapshot, 43.0% of US private establishments paid every two weeks and 27.0% every week, so 70% ran a pay cycle of two weeks or less (our arithmetic; BLS, 2023).

Signal processing has a name for what a month-end balance does to such a cycle. The sampling theorem holds that, to reconstruct a signal free of aliasing, “the sampling rate must be at least twice the signal’s bandwidth” (Nyquist–Shannon sampling theorem). Sample more slowly and the result contains “low frequency components that are not present in the original one” (Aliasing). A fortnightly payroll observed once a month aliases into a phantom cycle about 5.7 months long (our arithmetic). Accountants meet it in another form: biweekly pay means 26 paydays a year (BLS, 2014), so two months in a typical year carry three paydays, and those months look like a deterioration in a month-end series.

Weekly observation is exactly twice the frequency of a fortnightly payroll, the slowest rate that resolves it. The theorem assumes a smooth wave, and cash moves in discrete payments, so a weekly forecast shows which week is short but cannot say which day. In a tight week the answer is daily tracking, which PKF O’Connor Davies recommends for “large or material disbursements” (PKF O’Connor Davies).

Most small businesses have little room for that error. The JPMorgan Chase Institute’s study of 597,000 small businesses with Chase business accounts found that the median one held 27 days of outflows in cash, and a quarter held fewer than 13 days (JPMorgan Chase Institute, 2016). For that quarter, a fortnight without receipts would empty the account, and no month-end figure would show which fortnight.

Month-end balances can look comfortable while one week cannot cover a payroll

Suppose, hypothetically, a software company selling to businesses runs close to breakeven. It pays a fortnightly payroll of $165k, rent and software of $45k at the start of each month and $12k of other bills each week, and renews an annual contract for $85k in week 10. Customers pay $470k in the last week of each month, and card payments bring in $8k a week. The quarter follows a 4-4-5 calendar, and the company starts it with $450k.

A hypothetical company with comfortable month-ends and a thin week, $ thousands

Week	Receipts	Payroll	Other payments	Net flow	Closing cash
1	8	165	57	−214	236
2	8	–	12	−4	232
3	8	165	12	−169	63
4 (month-end)	478	–	12	+466	529
5	8	165	57	−214	315
6	8	–	12	−4	311
7	8	165	12	−169	142
8 (month-end)	478	–	12	+466	608
9	8	165	57	−214	394
10	8	–	97	−89	305
11	8	165	12	−169	136
12	8	–	12	−4	132
13 (month-end)	478	165	12	+301	433

Source: CX Cash calculation for a hypothetical company. Months follow a 4-4-5 calendar (weeks 1 to 4, 5 to 8 and 9 to 13). Payroll is loaded (wages, employer taxes, benefits) and makes up 75% of payments, close to Kruze’s 76%.

A monthly model of this company shows month-end balances of $529k, $608k and $433k and a net burn of about $6k a month, which reads as 76 months of runway. The weekly view shows $63k in week 3, 85% below the lowest month-end. Divide that lowest weekly balance by one payroll run and the company holds 0.38 of a payroll in week 3, against 2.62 at the lowest month-end.

The weekly view also explains why month 3 closes $175k below month 2. A monthly reader could take that for a deteriorating business, but a third payroll and the annual renewal land in a five-week month. It also names the real risk: in week 13 the third payroll and the month’s collections fall in the same week, and if customers pay one week late, the week closes at minus $37k with a payroll due. The calculator below runs the same test on any opening balance and 13 weekly net flows, and marks the tightest week.

An accounts receivable forecast dates receipts by each payer’s days to pay

The company dates its own payments, but customers date its receipts, and the week-13 risk sits there. Days sales outstanding (DSO), a balance divided by a sales rate, is a poor guide to those dates. France’s payment-delays observatory warns that customer days measured from balance sheets mix contractual terms and late payments indistinguishably (our translation; Banque de France, 2025).

Each payer’s record keeps the two apart: the term it applies to the company, and its habit of lateness beyond that term. Since April 2017, large UK companies have reported twice a year “the average number of days taken to make such payments” and the share paid after the agreed period (SI 2017/395). We analysed the 11,859 usable reports for periods ending in 2025, all self-reported and unaudited: the median company took 32 days to pay and paid 15% of payments late. Late share and days to pay correlate at 0.33, so lateness accounts for about a ninth of the variation in days.

Four large UK buyers, fast or slow, punctual or late

Buyer (reporting period)	Average days to pay	Payments later than agreed terms
HSBC UK Bank (Jan–Jun 2026)	12	1%
Salesforce UK (Feb–Jul 2026)	27	36%
Jaguar Land Rover (Oct 2025–Mar 2026)	57	33%
Nestlé UK (Jan–Jun 2026)	76	6%

Source: each company’s filing on the UK payment practices register, as of 3 October 2026.

Nestlé UK is slow but punctual, Salesforce UK fast but often late: one average lateness added to every due date gets both wrong. The filings also give the terms small suppliers get: 5 days at Tesco below £250K of annual business (Tesco Stores, 2026) and 30 days at Nestlé UK (Nestlé UK, 2026). Forecast at Nestlé’s 76-day average, a small supplier’s invoice issued at the start of week 1 lands in week 11. On its 30-day terms, the cash probably arrives in week 5.

Each payer’s record becomes a weekly curve, the share of an invoice paid in each week after issue, applied to open and expected invoices. The curve holds until the payer’s circumstances change. Jaguar Land Rover missed agreed terms on 70% of payments in October and November 2025, after a reported cyber incident, and on 12% from December to March (Jaguar Land Rover, 2026). A weekly comparison of forecast and receipts by payer catches such a shift in the week it happens.

Thirteen weeks is a calendar convention, so the fix should set the horizon

Weekly settles the time step and payer records the receipt dates, but neither sets the length. Thirteen is a unit of the accounting calendar; we found no forecasting research that singles it out. The 4-4-5 calendar, common in retail and manufacturing, “divides a year into four quarters of 13 weeks”, each split into two four-week months and one five-week month (4–4–5 calendar). US tax rules allow a 52-53-week year that “must always end on the same day of the week” (IRS Publication 538). A 13-week forecast therefore spans one fiscal quarter of 91 days, against 91.3 days for an average calendar quarter.

Neither convention says how far a particular company needs to see. Lord Walker’s test, the nature of the company’s business, suggests a practical rule: reach past the lowest week by at least the time the slowest available fix takes. A company with an undrawn credit line needs less. One whose fix is a new equity round needs more, so the 13-week view sits beside a monthly runway model.

Lenders judge the forecast by its variance, and boards can borrow the test

Lenders have written into their contracts how to tell whether a solvency forecast is right. Accelerate Diagnostics’ debtor-in-possession (DIP) term sheet of May 2025, for a facility of up to about $36.9M, required “a thirteen (13)-week cash flow forecast” and an update every other Friday. Receipts and disbursements were “tested every other week on a cumulative basis”, subject to a 15% permitted variance (Accelerate Diagnostics, 2025).

Li-Cycle’s DIP term sheet of the same month, under Canada’s insolvency regime, asked for a rolling 13-week budget and a variance report every Friday, with management commentary on any line that moved by 10% or more. Over rolling four-week test periods, disbursements could not exceed 110% of budget and receipts could not fall below 90%, and an adverse deviation beyond that tolerance was an event of default (Li-Cycle, 2025). Fisker, in an April 2024 forbearance agreement, undertook not to spend money “for any purpose other than as set forth in the Approved Budget”, its 13-week budget, and to appoint a chief restructuring officer to oversee compliance (Fisker, 2024).

These contracts bind distressed borrowers only, but the method needs no lender. Keep each week’s forecast, set it beside the actual week, record the miss by line and explain any line that misses by more than Li-Cycle’s 10%. In a DIP, a breach can stop the funding. A venture-backed company faces no such default, and the cost is softer: on our reading, a board that has seen misses go unexplained has less reason to believe the next forecast.

Does a funded startup need more than a runway model?

The best case against the weekly forecast comes from Paul Graham’s 2015 essay Default Alive or Default Dead? His first question to a startup: “Assuming their expenses remain constant and their revenue growth is what it has been over the last several months, do they make it to profitability on the money they have left?” (Graham, 2015). That is a long-horizon test of the whole trajectory, and for a company with two years of cash it is the right first question. Even a treasury-software vendor concedes the point: “If you run a company with steady cash inflows and a high valuation, a short-term model will not be as essential” (Ripple Treasury). When the lowest week still covers several payrolls, weekly updates add little.

It is weaker on one assumption: that the cash on the balance sheet can be spent. On 9 March 2023, Silicon Valley Bank lost over $40 billion of deposits in a single day. Its depositors were concentrated among venture capital investors and technology firms, and its management expected to lose over $100 billion more the next day. The two days together came to roughly 85% of the deposit base. Wachovia’s failure in 2008 had involved about $10 billion of outflows over 8 days, so SVB’s run moved more than 30 times faster per day (our arithmetic; Federal Reserve, 2023).

At the end of 2022, about 94% of SVB’s deposits were uninsured. Regulators closed the bank on the morning of Friday 10 March, and depositors learned only on Sunday 12 March that they would have “access to all of their money starting Monday, March 13” (Treasury, Federal Reserve and FDIC, 2023). For that weekend, months of runway mattered less than which bank held the next payroll.

The two views are therefore complements. A funded startup can run the light version: the monthly runway model, plus a 13-week view of cash by bank account, refreshed monthly and switched to weekly once the lowest week covers fewer than two payrolls. That threshold is our rule of thumb rather than a published standard; two fortnightly payrolls span 28 days, close to the 27-day median buffer in the JPMorgan Chase sample of small businesses.

The founder reads the lowest week; the board asks for its date

A founder who prepares the forecast builds it by the direct method: payments on the dates the company sets, receipts on the dates each payer’s record predicts. The figure to read is the lowest week, divided by one payroll run, with the opening balance split by bank and by insured and uninsured amounts. In a short week, payroll and payroll taxes go out before other creditors, since the IRS treats the reverse as a sign of willfulness. Suppliers can wait, at a statutory price. In the UK, late payers owe interest at 8% plus Bank of England base rate (GOV.UK). In the EU they owe the reference rate plus at least 8 points, and at least €40 per late payment (Directive 2011/7/EU). The free 13-week cash flow model below is a starting point.

A director has three requests to make. The first is the lowest week and its date, alongside the months of runway. The second is last quarter’s 13-week forecast set against the actuals, with the misses explained by line and by payer. The third is the weekly view in any quarter with a three-payday month or large annual payments, even when runway is long.

A dated lowest week leaves time to act

A 13-week cash flow forecast asks what courts, lenders and the IRS ask: whether the company can pay what falls due in each week. Its weak point is the customers’ dates. In the hypothetical company, a one-week slip in collections would turn the $433k close in week 13 into a $37k shortfall with a payroll due. Only each payer’s record, checked against receipts every week, shows how likely that slip is.

Sources

• Accelerate Diagnostics (2025), DIP term sheet, Exhibit 10.2 to Form 8-K filed 8 May 2025.

• Banque de France, Observatoire des délais de paiement (2025), Rapport annuel 2024.

• Board of Governors of the Federal Reserve System (2023), Review of the Federal Reserve’s Supervision and Regulation of Silicon Valley Bank.

• BNY Corporate Trustee Services Ltd v Eurosail-UK 2007-3BL plc [2013] UKSC 28, judgment of 9 May 2013.

• Matt Burgess (2014), How frequently do private businesses pay workers?, Beyond the Numbers 3(11), Bureau of Labor Statistics.

• Directive 2011/7/EU of the European Parliament and of the Council of 16 February 2011 on combating late payment in commercial transactions.

• Financial Accounting Standards Board (2014), Accounting Standards Update 2014-15, Going Concern (Subtopic 205-40).

• Fisker (2024), Form 8-K filed 22 April 2024 on its forbearance agreement.

• GOV.UK, Late commercial payments: charging interest and debt recovery.

• Paul Graham (2015), Default Alive or Default Dead?, paulgraham.com.

• Insolvency Act 1986 (UK), sections 123 and 214.

• Insolvenzordnung (Germany), §§ 15a, 17, 18 and 19.

• Internal Revenue Service, Employment taxes and the Trust Fund Recovery Penalty (TFRP) and Publication 538, Accounting Periods and Methods.

• JPMorgan Chase Institute (2016), Cash is King: Flows, Balances, and Buffer Days.

• Kruze Consulting, Startup Payroll Costs and Tax Budgeting for New Hires.

• Li-Cycle Holdings (2025), DIP term sheet, Exhibit 10.1 to Form 8-K filed 19 May 2025.

• PKF O’Connor Davies, A CFO’s Lifeline: Mastering the 13-Week Cash Flow Forecast.

• The Reporting on Payment Practices and Performance Regulations 2017 (SI 2017/395), as amended.

• Ripple Treasury, How to Use a 13-Week Cash Flow Model.

• US Bureau of Labor Statistics (2023), Length of pay periods in the Current Employment Statistics survey.

• US Treasury, Federal Reserve and FDIC (2023), joint statement of 12 March 2023.

• UK payment practices register: full export of 3 October 2026, and the filings of HSBC UK Bank, Salesforce UK, Tesco Stores, Jaguar Land Rover and Nestlé UK.

• Uniform Commercial Code § 1-201, via the Legal Information Institute.

• Wikipedia, 4–4–5 calendar, Aliasing and Nyquist–Shannon sampling theorem; German Wikipedia, Zahlungsunfähigkeit.

The legal tests come from the statutes and judgments listed, lender practice from term sheets and agreements filed with the SEC, and the payroll and cash-buffer figures from the BLS, Kruze Consulting’s client data and the JPMorgan Chase Institute. The UK payment statistics are our analysis of the government’s full register export, using medians because the filings are self-reported. Where a figure carries no citation, or is marked “our arithmetic”, we computed it from the cited data. The company in the weekly table is hypothetical, and the translations from German and French are ours, so they carry no quotation marks.