How to Build a Simple Revenue Forecast

Build a reliable revenue forecast using historical data, growth assumptions, and seasonal adjustments for better cash flow planning.

1. Calculate your trailing 12-month baseline. Add up total revenue from the past 12 months and divide by 12. This becomes your monthly baseline. If you have less than 12 months of data, use what you have but flag the forecast as preliminary.
2. Apply a growth rate assumption. For established businesses, use 0-10% annual growth unless you have specific reasons for higher projections. Multiply your monthly baseline by (1 + annual growth rate ÷ 12) for each forward month. New businesses should model conservative, base, and optimistic scenarios.
3. Adjust for seasonal patterns. Look at month-over-month variations in your historical data. Calculate each month as a percentage of your annual average (e.g., December might be 120% of average, February might be 80%). Apply these multipliers to your growth-adjusted baseline.
4. Account for known changes. Add or subtract specific amounts for confirmed new contracts, lost customers, price changes, or product launches. Only include items with signed agreements or firm launch dates. Keep assumptions separate from historical patterns.
5. Build in forecast ranges. Create low/high scenarios at ±15-25% of your base forecast. Most businesses miss forecasts by 10-30%, so ranges matter more than precision. Update monthly with actual results and adjust future months accordingly.
6. Track variance and adjust methodology. Compare actual results to forecasted amounts each month. If you're consistently off by more than 20%, revisit your growth assumptions or seasonal adjustments. Good forecasts improve with iteration, not perfection.