Performance Rating Distribution Calculator
Calculate the expected number of employees in each performance rating category based on total headcount and a distribution model (forced distribution or normal bell curve).
Results will appear here.
Formulas Used
Employee Count per Tier:
Raw Counti = (Percentagei / 100) × Total Headcount
Floor Counti = ⌊ Raw Counti ⌋
Remainderi = Raw Counti − Floor Counti
Largest-Remainder Rounding ensures all employee counts are whole numbers and sum exactly to total headcount:
Deficit = Headcount − Σ Floor Counti
Add 1 to the Deficit tiers with the largest remainders.
Distribution Spread (σ): Standard deviation of target percentages across tiers — measures how evenly or unevenly the model distributes employees.
σ = √[ Σ(pi − p̄)² / n ]
Assumptions & References
- GE Vitality Curve (20/70/10): Popularized by Jack Welch at General Electric — top 20% rewarded, middle 70% developed, bottom 10% managed out. (Welch, J., Winning, 2005)
- Bell Curve (10/25/30/25/10): A symmetric normal distribution model commonly used in HR performance management systems.
- Top-Heavy (5/15/30/35/15): A right-skewed model used in organizations that emphasize development over differentiation.
- Largest-remainder method is the standard approach for apportioning fractional counts to whole numbers (used in electoral systems and HR analytics).
- Custom percentages must sum to exactly 100% (±0.5% tolerance for floating-point entry).
- This calculator assumes a closed system — all employees receive exactly one rating tier.
- Forced distribution models are controversial; research suggests they can reduce collaboration and morale (Scullen et al., Journal of Applied Psychology, 2005).
- Results are intended for planning and budgeting purposes only, not as a substitute for individualized performance evaluation.