A grade curve adjusts scores after grading, usually to raise the class average toward a target. Common methods add a flat number of points to every score, multiply every score by a fixed percentage, or shift the letter-grade thresholds down instead of changing the raw scores at all.
Flat-point curve
The instructor adds the same number of points to every student's score. If the highest score was 92% and the instructor wants the top score at 100%, every student receives +8 points. A 75% becomes an 83%.
Percentage (multiplicative) curve
Every score is multiplied by a fixed factor rather than shifted by a flat amount. This method raises high scores by more raw points than low scores, since the adjustment scales with the original score.
| Original score | Flat +8 curve | ×1.10 curve |
|---|---|---|
| 60% | 68% | 66% |
| 75% | 83% | 82.5% |
| 92% | 100% | 100% (capped) |
Scale-shift curve
Instead of changing raw scores, the instructor lowers the percentage thresholds for each letter grade — for example, moving the A cutoff from 93% to 88%. Raw scores stay the same on paper, but more students land in a higher letter-grade band.
Square-root and standard-deviation curves
A square-root curve takes the square root of a percentage (expressed as a decimal) and multiplies by 100, which disproportionately helps lower scores — a 64% becomes 80%. A standard-deviation curve maps scores onto a bell curve around the class average, which can lower some students' grades even as it raises others'. These methods are less common but appear in some math and science courses.
Curves are the instructor's choice, not a right
No grading policy guarantees a curve. If a syllabus does not mention one, assume none will be applied and calculate your grade from the stated scale. Ask the instructor directly rather than assuming a specific curve method in advance.
Grade Calculator Editorial Team
We create plain-language grading tools and educational guides, check every worked example against the underlying formula, and note where school or instructor policies can change the result.