Bell Curve Adjustment Calculator Formula

Understand the math behind the bell curve adjustment calculator. Each variable explained with a worked example.

Use the Bell Curve Adjustment Calculator

Formulas Used

Curved Student Score

curved_score = min(student_score + curve_points, max_possible)

Points Added

points_added = curve_points

Percentage Increase

pct_increase = curve_points / current_mean * 100

Variables

VariableDescriptionDefault
current_meanCurrent Class Average68
target_meanTarget Average78
student_scoreIndividual Student Score72
max_possibleMaximum Possible Score100
curve_pointsDerived value= target_mean - current_meancalculated

How It Works

How Bell Curve Adjustment Works

The simplest curve adds a flat number of points to every score, shifting the entire distribution upward.

Formula

Points Added = Target Mean - Current Mean

Curved Score = min(Original Score + Points Added, Maximum)

This preserves the spread and relative rankings while raising the average to the target. Scores are capped at the maximum to prevent exceeding 100%.

Worked Example

Class average is 68, target is 78. A student scored 72 on a 100-point scale.

current_mean = 68target_mean = 78student_score = 72max_possible = 100
  1. 01Points added: 78 - 68 = 10
  2. 02Curved score: min(72 + 10, 100) = 82
  3. 03Percentage increase: 10 / 68 x 100 = 14.7%

Ready to run the numbers?

Open Bell Curve Adjustment Calculator