Grade Curve Calculator: Five Curving Methods for Teachers
Your class took an exam. The average was lower than you expected. You have decided to curve the grades. Now you need to figure out which curve method to use and what each student’s adjusted score will be.
This calculator gives you five different ways to curve: add points, increase by percentage, scale the highest score to 100%, use a linear curve, or apply a statistical z-score transformation. Enter a raw score, choose a method, and see the curved result immediately. You can also check what raw score a student would need to achieve each letter grade after the curve.
When to Use This Calculator
This tool is for teachers who have already decided to curve grades and need to figure out how to apply the curve.
If you are still deciding WHETHER to curve, start with the class average calculator. That tool provides the class mean, median, and distribution, which indicate whether a curve is appropriate. Once you have decided to curve, come here to choose a method and see the results.
This calculator does not make the curving decision for you. It applies whichever method you choose. You can experiment with different methods, see what they do to the distribution, and pick the one that makes sense for your situation.
The five methods range from simply adding 5 points to everyone to complex, statistical z-score normalization. Each has different effects on the grade distribution.
The Five Curving Methods
Add Points
The simplest method. You pick some points and add them to every raw score.
Example: Raw score 78% + 5 points = 83% curved.
How it works: Every student gets the same boost. If you add 5 points, a student with 65% becomes 70%, and a student with 90% becomes 95%. The gaps between students stay the same. If Student A scored 10 points higher than Student B before the curve, they still score 10 points higher after.
When to use it: When you want a simple, transparent boost that is easy to explain. “I’m adding 5 points to everyone’s score.” Students understand it immediately. Use this when the test was uniformly harder than you intended, but still fairly differentiated students.
In the calculator: Enter the number of points to add in the “Add points” field.
Percent Increase
Multiply every raw score by a percentage increase.
Example: Raw score 78% × 1.10 (10% increase) = 85.8% curved.
How it works: Students with higher raw scores get a larger absolute boost. A 10% increase gives a student with 80% an 8-point boost to 88%, but a student with 60% only gets a 6-point boost to 66%. This method rewards students who scored higher originally.
When to use it: When you want to boost scores proportionally rather than equally. If you think higher-performing students deserve a greater advantage because they demonstrated greater mastery even on a difficult test, this method preserves those performance differences.
Watch out: This method can widen the gap between high and low performers. A 10% boost on a 90% is 9 points; on a 50%, it is only 5 points.
In the calculator: Enter the percentage increase, e.g., 10 for 10%, in the “Increase by percent” field.
Scale to Max
The highest raw score in the class is capped at 100%, and all others are scaled proportionally.
Example: If the highest score was 92%, then a 78% raw score becomes 78 ÷ 92 × 100 = 84.78% curved.
How it works: Find the highest raw score. That becomes the new 100%. The same factor scales up every other score. If the top score was 85%, everyone’s scores are multiplied by 100 ÷ 85 = 1.176.
When to use it: When you designed the test for a maximum of 100%, but the highest score fell short. Scaling to max ensures that at least one student gets 100%, and everyone else is adjusted proportionally. This is common when a test turned out harder than intended, but still had a clear top performer.
Watch out: If your highest scorer got 60%, scaling to max means they get 100%, and everyone else is doubled. This can overcompensate if the top score was very low.
In the calculator: Enter the highest raw score in your class in the “Highest score” field.
Linear Curve
Map your class means to a target mean and the highest score to 100%, preserving the shape of the distribution.
Example: Class mean is 72%, target mean is 80%, and the highest score is 95%. The calculator creates a linear transformation that shifts 72 → 80 and 95 → 100, and all other scores shift proportionally.
How it works: This uses a linear equation (y = ax + b) where the class mean maps to your target mean, and the highest score maps to 100%. The distribution’s shape stays the same. If scores were normally distributed before, they still are after. The whole distribution shifts upward.
When to use it: When you want to move the class average to a specific target without distorting the distribution. If you expected a class average of 80% but got 70%, this method shifts everyone up by the same amount needed to hit that 80% target while keeping the spread intact.
In the calculator: Enter your class means, target mean, and highest score in the “Linear curve” fields.
Z-Score Bell Curve
Statistical normalization. Converts raw scores to z-scores, then scales them to a target mean and standard deviation.
Example: If the class mean is 70% with a standard deviation of 15%, and you want a target mean of 80% with a standard deviation of 10%, each student’s z-score is calculated as z = raw – 70 / 15, then transformed to the new distribution: curved = 80 + z × 10.
How it works: This is the most statistically rigorous method. It transforms your actual distribution into a target distribution with a specific mean and standard deviation. A student who was 1 standard deviation above the class mean stays 1 standard deviation above the target mean. The shape of the distribution can change wider or narrower depending on your target standard deviation.
When to use it: When you want precise statistical control over the curved distribution. If your institution expects a certain average and spread, e.g., mean 75%, standard deviation 12%, this method delivers exactly that. Common in large courses where grade distributions are standardized.
Watch out: This is the least intuitive method for students. “I used a z-score transformation” is harder to explain than “I added 5 points.”
In the calculator: Enter class mean, class standard deviation, target mean, and target standard deviation in the “Z-score” fields.
The “What If” Feature
Below the main result, there is a “What if” calculator. Enter a hypothetical raw score, and it shows you what that score would become after applying your chosen curve.
This is useful for quick checks. “If a student got 85% raw, what would that be curved?” You do not have to apply the formula manually. Just type 85 in the what-if box and see the curved result instantly.
It is also useful for explaining curves to students. If a student asks, “What would I have needed to get an A?”, you can enter different raw scores in the what-if box until you find the threshold.
The what-if result updates every time you change the curving method or parameters.
The “Needed Scores” Table
This table shows what raw score a student would need to achieve each letter grade after the curve is applied.
For example, if you are using “Add 5 points” and the curve moves the B threshold from 83% to 88%, the table shows “To get a B, a student needs a raw score of 83%.”
This helps set expectations or reverse-engineer grade cutoffs. If you want to ensure that students who score at least 75% raw earn a B after the curve, adjust the curve method until the required score table shows 75% as the B cutoff.
The table updates automatically when you change methods or parameters.
The Score Mapping Table
The bottom of the calculator displays a full mapping table: raw scores from 0 to 100 in 5% increments, along with the corresponding curved score, letter grade, and GPA for each.
This gives you a complete picture of how the curve transforms the entire range of possible scores. You can scan the table to see “A raw 70% becomes 78% curved, which is a C+.”
Use this table to verify the curve does what you expect across the full range, not just at the mean or at specific letter grade boundaries.
Clamp Mode: Capping Scores at 100%
Some curving methods can produce curved scores above 100%. For example, if you add 10 points and a student got 95% raw, their curved score would be 105%.
The “Clamp” setting is enabled by default and caps all curved scores at 100%. If the clamp is on, a 105% becomes 100%.
If you turn off the clamp, scores can exceed 100%. Some teachers allow this as extra credit. Others cap at 100% because that’s the maximum defined grade.
Choose based on your grading policy. Clamp-on is more common.
Ethical Considerations
Curving grades is a teacher’s decision, and it is not always the right choice. Curves can help when a test is unexpectedly hard. Still, they can also mask problems, leave questions unclear, fail to teach material well, or unfairly advantage students who benefited from a low-performing class.
This calculator does not make that ethical decision for you. It is a tool that applies whichever method you choose. Before using it, ask:
- Was the test actually harder than intended, or did students not prepare?
- Does the curve maintain fairness between students, or does it distort performance differences?
- Are you curving because the class performed poorly, or because you need to fit a grade distribution?
Use the class average calculator to see your class statistics first. Curve only if the data supports it.
FAQ: Grade Curve Calculator
Which curving method should I use?
It depends on your goal. Adding points is the simplest and most transparent. Percent increase rewards higher performers proportionally. Scaling to the maximum is appropriate when the top score is below 100%. A linear curve is best when you have a specific target mean in mind. Z-score is for statistical precision. Try each method and see which result makes sense for your class distribution.
How is this different from the class average calculator?
The class average calculator shows you the statistics, mean, median, and distribution to help you decide whether to curve. This calculator applies the curve using one of five methods. Use the class average first to analyze, then use this tool to apply the curve you’ve chosen.
Can I use this for individual student scores?
Yes. Enter the raw score in the main calculator, choose your method, and see the curved result. The what-if feature also lets you check multiple scores quickly.
Does this calculator store my class data?
No. The calculator runs in your browser. Nothing is saved unless you use a share button. If you refresh the page, your settings reset.
What if my curved scores go above 100%?
Use the clamp setting. Clamp on default caps curved scores at 100%. Clamp off allows scores above 100% if your grading policy permits extra credit.
Can students see this calculator?
Yes, it is public. But they can not see your class statistics’ mean and standard deviation unless you share them. Students could use this to understand how different curving methods work, but they can not apply a curve to their own score without knowing the method and parameters you chose.
Related Tools
Class Average Calculator: Use this first to calculate class statistics and decide whether a curve is warranted. It shows the mean, median, mode, minimum, maximum, and percentiles.
Curving is a teaching decision, not just a math problem. This calculator handles the math you provide the judgment.
Choose a method, enter your parameters, and see the results. Check the what-if scores, review the needed-scores table, and scan the full mapping table. When the curve looks right, apply it to your class.
The calculator gives you five methods because there’s no single “correct” way to curve. Pick the method that fits your situation.