Free sales forecast template

Prefer to work in a spreadsheet? This template forecasts the next 12 months from up to three years of monthly sales, using formulas you can read and change.

Reviewed October 2026

What's in the template

• Your data: enter up to 36 months of sales, oldest first. The example numbers are made up; type over them.
• Trend: a straight-line trend fitted with the spreadsheet's own TREND function.
• Seasonal factors: for each calendar month, how far sales usually run above or below the trend, as a ratio.
• Forecast: the trend extended 12 months ahead, multiplied by each month's seasonal factor, with a simple total and growth rate.

It works in Microsoft Excel, Google Sheets (File, then Import) and Apple Numbers. Nothing in it is locked, so you can see and change every formula.

How to use it

1. Put your month labels in column A and sales in column B, replacing the example numbers. Leave blank any rows you don't need.
2. Make sure you have at least 24 months for the seasonal factors to mean much. With fewer, the template still works but the seasonal factors are less reliable.
3. Read the forecast on the Forecast sheet. Adjust it for anything you know is coming, such as a price change, and note why.

For a quicker answer, or to compare several methods automatically, paste the same numbers into the forecast tool. It runs entirely in your browser, and nothing is uploaded.

How it calculates

This template uses a classic approach, sometimes called trend-times-seasonal decomposition:

1. Fit a trend line through all months.
2. Divide each month's sales by the trend for that month, then average those ratios for each calendar month to get its seasonal factor.
3. Extend the trend forward and multiply by each month's seasonal factor.

It's simple and transparent. It assumes the seasonal pattern grows with your sales and the trend is a straight line, so check the result against your own sense of the business. See forecasting methods explained for other approaches.