Guide · 2026-11-03
13-week cash flow forecast: build your own spreadsheet, use a template, or buy software?
Once you decide to forecast cash weekly, there are three realistic ways to do it. None is right for everyone, so here is a straight comparison.
| Build your own spreadsheet | Excel template | Cash-flow software (SaaS) | |
|---|---|---|---|
| Cost | Free | One-time, typically $20–$50 | Monthly subscription |
| Setup time | Many hours to build and debug | Under an hour | An hour or two, plus connecting accounts |
| Data entry | Manual | Manual (lists you maintain) | Mostly automatic from your accounting system |
| Flexibility | Total | High — it's still Excel | Limited to the product's model |
| Main risk | Formula errors nobody notices | Template doesn't fit your business | Paying monthly for features you don't use |
| Data location | Your computer | Your computer | Vendor's cloud |
Build your own if…
you're comfortable with Excel, your cash flows are simple, and you enjoy building tools. Budget a few evenings, and test the edge cases: fortnightly payroll, items on the 31st, quarterly payments.
Use a template if…
you want a working weekly forecast this week, prefer a one-time cost, and want your financial data to stay in a file you control. Choose one that schedules recurring items for you — otherwise you're back to copying numbers across 13 columns.
Buy software if…
you have many transactions, already use cloud accounting with a supported integration, and the monthly fee is small compared with the time saved. Software shines when the data entry is the bottleneck.
What matters more than the tool
Whichever you pick, the forecast is only useful if you update it every week, use realistic payment dates and compare it with what actually happened. A simple model you roll forward every Monday beats a sophisticated one you open once a quarter.
Want this done for you?
CashRunway 13 sits in the template column: a one-time purchase that automates the scheduling without a subscription or bank connection.