How to Forecast Monthly Sales in Excel

1. Prepare the source and scope

Import sales.csv into a new worksheet with headers in row 1. Leave the source columns in their original order for the formulas below. Review the data dictionary before choosing the reporting period. Keep identifiers as text and convert numeric columns explicitly. Save a working copy so you can return to the original fixture.

2. Build the calculation

Use the twelve 2026 observations only. Add month indices 1 through 12 in J14:J25 and fit a linear forecast for month 13. Compare against a holdout period before using a model operationally.

=FORECAST.LINEAR(13,D14:D25,J14:J25)

3. Reconcile and interpret the output

The expected check is january 2027 illustrative forecast: 26000 USD. The 2026 sample increases by 1,000 per month. This extrapolation assumes that trend continues and ignores seasonality. If your result differs, inspect the selected rows, data types and date filters before changing the formula.

4. Adapt the workflow to a recurring report

Replace the sample with a copy of your own source, retaining the same column meanings and units. Extend bounded ranges to include new rows, refresh PivotTables where used, and compare the result to an independent source total. Record the reporting period and any exclusions beside the output. Do not fit both years as one smooth trend: the sample contains a level change between years.