As a forecasting and planning manager, I want a custom calendar system that divides the year into 12 fixed 28-day "months" (each exactly 4 weeks), grouped into 4 quarters (each 84 days), with each period always starting on a Monday, and an uplift mechanism to extrapolate metrics over actual Gregorian days, so that I can achieve consistent, predictable forecasting and planning rhythms while maintaining accurate retrospective reporting from stored data.

Description

• Core Structure: Override the default Gregorian calendar for internal views. Use 336 core days per year (12 × 28), with uplifts to bridge the ~29-day annual shortfall (or ~30 in leap years).
• Monday Starts: Automatically calculate and enforce Monday as the start day for each month, quarter, and year, regardless of Gregorian alignment. For example, if a Gregorian period starts mid-week, adjust the custom period backward or forward and apply up- or downlifts to compensate for any "lost" or overlapping days.
• Uplift Mechanism: Build an automated extrapolation function based on partial data. For a period with D_actual days vs. 28 custom days, uplift factor = D_actual / 28 (e.g., 1.107 for 31-day months). Apply this to metrics like work completed, KPIs, or progress (e.g., if 80% done in 28 days, project 88.6% for 31 days). Use historical averages from stored data for non-linear adjustments (e.g., accounting for holidays).
• Integration: Ensure all actual data remains stored unaltered in the tool's database for Gregorian-based retrospective reports (e.g., for compliance). Provide toggle views: custom (for planning/forecasting) vs. actual (for tracking/reporting).
• Automation: Include scripts or formulas for date calculations, uplift factors, and visualizations like dashboards showing uplifted vs. actual metrics.

Acceptance Criteria

• System correctly generates custom periods for any given year (tested on 2025: Q1 custom start on Dec 30, 2024, to align with Jan 1 Wednesday).
• Uplifts accurately scale metrics in forecasts (e.g., manual test: 100 units in 28 days uplifts to ~108.6 for a 30-day month).
• Tool preserves raw data integrity; retrospective reports ignore custom logic and use Gregorian dates.
• Handles edge cases: Leap years, variable month lengths (28-31 days), holidays (e.g., no uplift distortion).
• User interface allows easy switching between views; errors flagged if uplifts exceed reasonable thresholds (e.g., >20% variance from historical norms).
• Performance: Calculations run in <5 seconds for annual forecasts.

Business Value

This feature delivers high operational efficiency by reducing planning variability (e.g., consistent 20 workdays per "month" vs. Gregorian's 18-23), potentially saving 5-10% in forecasting time per quarter. It minimises errors in projections, supports better resource allocation, and ensures compliance without dual systems.