A cash flow forecast is the spreadsheet that tells you whether you'll run out of money before you run out of month. It's the most important financial model most small and mid-size businesses either don't have or have but don't trust.
This guide shows you how to build a 12-month cash flow forecast in Google Sheets that's simple enough to actually maintain and accurate enough to make decisions from.
The Structure
A cash flow forecast has three sections: Cash In (inflows), Cash Out (outflows), and the running cash balance. Set up months as columns (January through December) and line items as rows. Column A holds the labels.
The basic flow:
- Opening Cash Balance (start of month)
- Plus: Total Cash In
- Minus: Total Cash Out
- Equals: Closing Cash Balance (which becomes next month's opening balance)
Forecasting Cash Inflows
Break inflows into line items that match how your revenue actually works. For a SaaS business: Monthly Recurring Revenue, New Sales, and One-Time Revenue. For a services business: Retainer Revenue and Project Revenue. For a product business: Product Sales and Wholesale Revenue.
For each line item, enter your best estimate for each month. If you have historical data, base it on that. If you're forecasting growth, add a growth rate assumption:
=B3*(1+$B$1)
Where B3 is last month's revenue and B1 is your monthly growth rate assumption. Lock the growth rate cell with $ so you can change one number and the whole forecast updates.
Forecasting Cash Outflows
List your fixed costs (rent, salaries, software subscriptions) and variable costs (COGS, marketing spend, contractor fees) as separate line items. Fixed costs are easy — enter the same number across all 12 months. Variable costs should be tied to revenue or volume assumptions.
For example, if your COGS is 30% of revenue:
=B5*0.30
Where B5 is total revenue for that month. Now COGS updates automatically as your revenue forecast changes.
The Rolling Cash Balance
Opening balance for January is your current cash on hand. Closing balance for January:
=B2+B15-B25
Where B2 is opening balance, B15 is total cash in, and B25 is total cash out. February's opening balance is January's closing balance:
=C2
Where C2 is the closing balance cell from January. Copy this pattern across all 12 months. The forecast now chains automatically — change any assumption and the entire 12-month balance updates.
Scenario Planning
Add an Assumptions table above or beside your forecast with key inputs: growth rate, COGS %, headcount additions, and one-time items. Reference these cells in your formulas instead of hardcoding numbers. Then build two scenario tabs — Base Case, Upside, and Downside — by copying the forecast and adjusting the assumption inputs.
This lets you answer "what happens to our cash position if growth slows to 5% instead of 10%?" in about 30 seconds.
Flagging Cash Crunches
Add conditional formatting to your Closing Cash Balance row: red if below zero, amber if below a minimum threshold (e.g., one month of expenses). This makes cash crunches visible immediately without reading every number.
The Easy Way: Using SheetXAI in Google Sheets
Example 1: You have revenue and expense data already in the sheet.
"I have monthly revenue and expense data on Sheet 1. Build a 12-month cash flow forecast with an assumptions table for growth rate and COGS percentage, and flag any months where closing cash goes below $50,000."
SheetXAI reads your data, builds the forecast structure, links the formulas to assumption inputs, and adds the conditional formatting.
Example 2: Your financial data lives in your accounting software.
"Pull this year's actuals from QuickBooks and use them as the base for a 12-month cash flow forecast with scenario planning for base, upside, and downside cases."
SheetXAI connects to QuickBooks, pulls historical actuals, and builds the full forecast with scenarios.
Try SheetXAI free and see what it builds for you.
Published May 2026. See also: How to Build a Profit and Loss Report in Google Sheets, How to Build a Budget vs. Actuals Report in Excel, and Google Sheets AI Guide.
