Startup founders should build a 13-week cash flow forecast from reconciled spendable cash, then map actual cash in and out week by week. A 13-week cash flow forecast is a quarter-ahead projection that shows ending cash for each week. It answers a simple question: will we have enough cash each Friday to pay bills. The structure is small enough to maintain and detailed enough to catch a shortfall early.
Table of Contents
- What should the model look like?
- Where do you start Week 1?
- How do you time cash in and out?
- Why 13 weeks instead of monthly?
- How do you keep it accurate and useful?
What should the model look like?
Build one label column plus 13 weekly columns headed by week-ending date, often Friday, plus a total column. Use sections for beginning cash, receipts, disbursements, net flow and ending cash.
Each week follows one rule: opening cash plus receipts minus disbursements equals closing cash. That closing balance becomes the next week's opening balance, which reveals the lowest-cash week. Business-Software.com describes this layout in its forecast structure guide.
Where do you start Week 1?
Start with the reconciled operating bank balance on day one of Week 1. Exclude restricted funds and uncleared deposits, because the accounting-system balance overstates spendable cash.
This starting point matters more for startups than for larger firms. A small restricted grant or pending deposit can hide a payroll gap. Universal Funding makes this starting-balance rule explicit in its 13-week template guide.
How do you time cash in and out?
Use the direct method. Place customer collections, payroll by pay date, vendor payments, debt service, taxes and one-time items in the week cash actually moves, not when revenue is earned or an expense is booked.
For receipts, schedule from the accounts-receivable aging report using each customer's actual days-to-pay. A "net 30" customer who pays in 45 days belongs in week 7, not week 5.
- List open invoices by customer and due behavior
- Assign each collection to its cash-receipt week
- Place payroll in its check week, even when a month has three payrolls
- Put rent, vendors, loan payments, taxes and one-offs in their payment weeks
Why 13 weeks instead of monthly?
Thirteen weeks covers one quarter. That span is long enough to catch payroll collisions, large tax or vendor payments and 60-day collections, but short enough to stay actionable.
Monthly forecasts hide intra-month gaps. Payroll on the 15th can fail even when receipts on the 28th make the month look safe. Universal Funding explains that timing advantage in its 13-week template guide.
How do you keep it accurate and useful?
Operate it as a rolling forecast. Each week replace the finished week's projection with actuals, explain material variances, adjust forward assumptions, and add a new Week 13.
Then set a minimum cash floor and run base and downside cases for late collections or lost deals. Upflow recommends pre-agreeing responses before a breach in its CFO guide to the 13-week forecast. Agree triggers now: draw credit, defer spend, or accelerate collections.