How to Forecast Cash Flow for the Next 90 Days

Most small business owners check their bank balance and call that financial planning. The problem with bank balance as a planning tool is that it tells you where you are, not where you're going.

A 90-day cash flow forecast tells you where you're going. And it gives you enough lead time to change direction if you don't like what you see.

Why 90 Days Is the Right Window

Thirty days is too short. By the time you identify a problem, it's already a crisis. Twelve months is too long to be actionable with real confidence. Ninety days gives you:

• Enough forward visibility to see problems coming
• Enough lead time to act (collections, cost cuts, credit applications)
• Enough accuracy to make real decisions. Most of the inputs for the next 90 days are knowable

The Four Inputs

1. Starting cash balance

Your current cash across all business accounts. This is the starting point for the forecast.

2. Expected cash in (collections)

Project cash receipts week by week for the next 90 days:

• Current outstanding invoices: use your AR aging to project when each will be collected
• Recurring revenue (maintenance agreements, service contracts). These are predictable
• Expected new job revenue based on your pipeline and historical close rates

3. Expected cash out (payments)

Project cash payments week by week:

• Fixed obligations: payroll, rent, insurance, loan payments. These are known and don't change
• Variable expenses: materials, subcontractors, etc. Estimate based on projected revenue
• Tax payments: quarterly estimates and known due dates

4. One-time items

Any large, non-recurring cash flows you're aware of such as a major equipment purchase, a large deposit expected from a commercial client or an insurance premium renewal.

Building the Forecast

The simplest format: a spreadsheet or table with weeks as columns and rows for each cash in/out category. Run the cumulative balance across the bottom. The lowest point in the 90-day period is your minimum. If that number is below your operating cost floor, you have a problem to address.

You don't need accounting software or a financial model. A spreadsheet and two hours of initial setup are enough.

How to Keep It Current

Update the forecast monthly:

• Replace the completed month's actuals with the next month's projections
• Update outstanding invoices with current AR aging data
• Adjust variable expense projections based on known upcoming work
• Roll the window forward by one month

With a working forecast template, each monthly update takes 20–30 minutes.

Using the Forecast to Make Decisions

The forecast is only useful if you act on it. When the forecast shows a low point:

• More than 60 days out: push collections, adjust costs, line up credit proactively
• 30–60 days out: accelerate collections aggressively, defer discretionary spending
• Under 30 days: all of the above, plus evaluate emergency options

The Bottom Line

A 90-day cash flow forecast is not a complex financial model. It's a structured look at what you expect to come in and go out over the next three months. Build it once, update it monthly, and use it to make decisions before circumstances force your hand.