Math calculator
Percentage Calculator for Change and Ratios
Calculate percent of a number, percentage increase or decrease, what percent X is of Y, discounts, grades, money percentages, and Excel formulas.
FormulaPercent of number = percent / 100 x number; X as percent of Y = X / Y x 100; change % = (new - old) / old x 100
Formula
Percentage formulas
Percentage results depend on the base value you choose. For finance, taxes, grades, or loans, confirm the required base, rounding rule, and policy before making a final decision.
Percent of number = percent / 100 x number; X as percent of Y = X / Y x 100; change % = (new - old) / old x 100
15% of 240 is 15 / 100 x 240 = 36. A change from 80 to 100 is 25%.
SourcesThis calculator includes source notes, assumptions, and exclusions so the result is easier to verify before use.
Sources and assumptions
Source notes
This calculator includes source notes, assumptions, and exclusions so the result is easier to verify before use.
- Effective year
- Current rules
- Last verified
- 2026-06-18
Percentage results depend on the base value you choose. For finance, taxes, grades, or loans, confirm the required base, rounding rule, and policy before making a final decision.
Assumptions
- Paired values use the same unit, time period, or currency.
- Percentage change uses the old value as the denominator.
- Grade and test percentages are raw scored marks divided by total marks.
Not included
- Weighted course grading policies.
- Tax-law-specific percentage rules.
- Compounding interest, detailed loan amortization, or currency conversion.
FAQ8 common questions for this calculator.
FAQs
How does the Percentage Calculator calculate the result?+
For the Percentage Calculator, it uses the Percentage formulas: Percent of number = percent / 100 x number; X as percent of Y = X / Y x 100; change % = (new - old) / old x 100. 15% of 240 is 15 / 100 x 240 = 36. A change from 80 to 100 is 25%.
What information do I need to use the Percentage Calculator?+
Choose the percentage task first, then enter the paired values it asks for: percent and base number, part and whole, old value and new value, discount price, markup, or reverse percentage.
How accurate is the Percentage Calculator?+
Percentage results are arithmetic estimates from the paired values entered in the selected mode. They can become misleading when the base value is zero, negative, rounded, or not the same measurement period as the comparison value.
What should I check before using the Percentage Calculator result?+
Check which percentage mode you selected, whether the base value can be zero, and whether old and new values use the same unit and time period.
How do I calculate a percentage of a number?+
Multiply the number by the percentage and divide by 100.
How is percentage increase or decrease calculated?+
Subtract the old value from the new value, divide by the old value, then multiply by 100.
What percent is X of Y?+
Divide X by Y, then multiply by 100. For example, 25 is 12.5% of 200.
How do I calculate percentage discount or percent off?+
Multiply the original price by the discount percentage to find the savings, then subtract the savings from the original price.
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Math guide
How to use the Percentage Calculator
Choose the percentage question that matches the problem: percent of a number, part as a percent of whole, percentage change, discount, markup, or reverse percentage. The examples and formula tables help you avoid mixing up the base value with the result.
- 1
Choose percentage mode
Select whether you need percent of a number, part of whole, percentage change, discount, markup, or reverse percentage.
- 2
Enter matching values
Use values from the same unit and time period, especially for old-versus-new comparisons and grade or money examples.
- 3
Check the base value
Compare the result with the formula table so you know which number was the base, which was the part, and how rounding was applied.