Forecast high-demand capacity from last year's same-period…

Use reference class forecasting from last year's actual capacity during the same seasonal period rather than estimating from your current state when planning high-demand periods.

When This Fires

When planning commitments for upcoming high-demand periods identified by Audit the past 12 months of calendar data — rate each…
When your inside-view estimate for a future period feels optimistic relative to past experience
When seasonal patterns repeat but your planning doesn't account for them
Complements Start project estimates with reference class forecasting… (project-level reference class forecasting) with the seasonal application

Common Failure Mode

"This year will be different" — the seasonal version of the planning fallacy. You remember last December was overwhelming, but you believe this December will be better because [reason that sounds compelling but changes nothing structural]. The structural drivers of seasonal demand (holidays, fiscal year-end, weather, school schedules) don't change year to year. Your capacity during those periods won't either.

The Protocol

(1) For each upcoming high-demand period, pull your actual data from the same period last year: how many projects were active? How many completed? How many slipped? What was your stress level? (2) Use last year's actuals as your capacity ceiling: "Last December I completed 3 projects, not the 5 I planned. This December, plan for 3." (3) If you have multi-year data, use the average across years — this smooths out single-year anomalies. (4) Allow modest upward adjustment only for genuine structural changes: "I hired an assistant this year" justifies slightly higher capacity. "I feel motivated" does not. (5) When in doubt, plan for the lower end of historical capacity. Under-committing during high-demand periods is vastly less costly than over-committing.