A rolling forecast keeps the planning horizon constant by adding a month every time one closes. Paste monthly actuals and choose a method to project the next 12, 18 or 24 months and compare the outlook against the trailing twelve months.
How it works
Extend monthly actuals into a 12-, 18- or 24-month rolling forecast using run-rate, growth, linear trend or seasonal methods.
Seasonal: F(t) = A(t − 12) × (1 + YoY growth)
Trend: F(t) = b₀ + b₁·t (ordinary least squares on actuals)
Compound: F(t+k) = A(t) × (1 + monthly growth)^k
Run rate: F = average of the last 3 actual monthsCommon uses
- Monthly reforecasting after each close
- Revenue, volume and expense projections
- Cash and covenant planning between budget cycles
Worked example
The calculator above opens with this example. Change any input to see the results update instantly, or select Reset to return to these figures.
| Monthly actuals (oldest first) | 1,182,000 1,096,500 1,214,300 1,205,800 1,251,200 1,238,900 1,198,400 1,226,700 1,264,100 1,301,800 1,276,300 1,352,600 1,248,900 1,151,200 1,279,800 1,266,400 1,318,700 1,305,200 |
| Last actual month | 2026-09 |
| Forecast horizon | 12 months |
| Method | Seasonal (same month last year × growth) |
| Growth rate | 4% |
| Next 12 months forecast | $15,797,704 |
| Trailing 12 months actual | $15,190,100 |
| Growth vs. trailing 12 | 4.0% |
| Average forecast month | $1,316,475 |
Forecast runs Oct 2026 – Sep 2027.
Interpreting the results
- Seasonal works best for revenue and volume with a stable annual pattern (e.g., patient days, retail sales).
- Use linear trend when there is steady growth and little seasonality; check R² — below 0.5 means the trend explains little.
- Roll the forecast every month: drop the oldest actual, add the newest, and re-forecast the horizon.
Frequently asked questions
Which forecasting method should I choose?
Use run rate (the average of the last three months) for stable series, compound growth when you have a defensible growth assumption, linear trend when history shows a steady slope, and seasonal when the same months recur high or low each year. The seasonal method projects each month from the same month a year earlier, adjusted for growth.
How is a rolling forecast different from an annual budget?
An annual budget is set once and measured against a fixed fiscal year. A rolling forecast is updated every period and always looks the same distance ahead, so it reflects current run rates rather than assumptions made months earlier.
How much history do I need?
The calculator needs at least three months for run-rate, growth and trend methods and twelve months for the seasonal method. Twenty-four months or more gives a more reliable trend line and lets you confirm that seasonal patterns repeat.
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