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How to Calculate Grades: A Step-by-Step Guide for Teachers

Updated July 12, 2026 · 8 min read

Grading is one of the most repetitive parts of teaching. The math itself is simple, but doing it correctly and consistently across a full class set of quizzes, tests, and assignments takes real discipline. This guide walks through the exact formula used to turn raw scores into percentage grades, then covers the edge cases every teacher runs into: partial credit, extra credit, dropped scores, and curved grades.

The basic percentage formula

Every percentage grade comes from the same formula:

Percentage = (Points Earned ÷ Points Possible) × 100

If a quiz has 20 questions and a student answers 17 correctly, that is 17 ÷ 20 = 0.85, or 85%. If you prefer to count wrong answers, just subtract from the total first: 20 − 3 wrong = 17 right, then divide. Both approaches produce the same result — which is exactly how the QuickGrade calculator works when you type the number wrong.

Worked example: a 25-question test

1. Total points possible: 25
2. Student missed 4 questions, so points earned = 21
3. 21 ÷ 25 = 0.84
4. 0.84 × 100 = 84%

On a common US 10-point scale, 84% is a solid B. See our percentage-to-letter-grade guide for the full conversion chart.

Handling partial credit

Partial credit means a question is worth more than a single right-or-wrong point. Instead of counting whole questions, count points. If a 5-part short-answer question is worth 10 points and the student earns 7, record 7/10 for that question and add it to the running total of points earned and points possible for the assignment.

Keep the rule consistent: every question's earned points goes into the numerator, every question's possible points goes into the denominator. The final percentage is always earned divided by possible, times 100.

Extra credit the fair way

Extra credit only feels fair when the rules are written down before the assignment. Two common approaches:

• Bonus points on the same assignment. A 20-point quiz with a 2-point bonus question lets a student earn up to 22/20 = 110%. If your gradebook caps grades at 100%, note that explicitly.
• Separate extra-credit assignment. Add a small assignment (say, worth 5 points) that only adds to the numerator when completed, leaving the denominator unchanged.

Dropped scores

Many teachers drop the lowest quiz or homework score at the end of a term. To calculate a dropped-score average, remove the lowest score from both the earned and possible totals before dividing. Never drop just the numerator or just the denominator — that changes what the percentage means.

Curved grades

A curve is any transformation applied after the raw percentage is calculated. The two most common:

• Flat curve. Add the same number of points to every student. If the top score is 88, add 12 so it becomes 100 and every other score rises by 12.
• Square-root curve. New grade = √(raw grade) × 10. A raw 64 becomes 80. This raises low scores more than high ones.

Curves are a policy decision, not a math requirement. Only apply one when your assessment turned out harder than intended and you have written it into your syllabus.

Recording the final grade

Once you have a percentage, translate it to whatever format your school uses: a letter grade, a 4.0 GPA point, or a standards-based proficiency level. Our grading scales guide covers each system in detail.

Speed tips for grading a stack of papers

• Grade one question at a time across the whole stack, not one paper at a time. Your eye locks onto the answer key faster.
• Use QuickGrade with the "+1 Wrong" button so you never touch a calculator app while your hands are on the papers.
• Print the QuickChart once per assignment size and clip it to the top of the stack.
• Record percentages, not points, in your gradebook if you plan to mix assignments of different sizes. It prevents surprises at report-card time.

Ready to grade? Open the free grade calculator and try it with a stack of papers on your desk right now.