Percentage Calculator
Five tools on one page: measure increase or decrease between two values, find X% of Y, turn two amounts into a percent, add a percent to a total (tax, markup, tip), or take a percent off (sale price). Formulas and examples sit below each calculator.
Calculate the Percentage increase/decrease
What is X% of Y?
X is what % of Y?
Add X% to Y
Subtract X% from Y
How to use this page
Pick the calculator that matches your question, enter two values (or a percent and an amount), and read the result instantly. Scroll to the matching section below for the exact formula and a worked example.
- Percentage increase or decrease — You have a before and an after; you want the % change relative to the start.
- What is X% of Y? — You know the rate and the base; you want the portion (e.g. commission on a sale).
- X is what % of Y? — You have two amounts; you want the first as a percent of the second.
- Add X% to Y — You want the new total after increasing Y by X% of itself (tax, markup, tip on subtotal).
- Subtract X% from Y — You want the price after taking X% off Y (single discount).
Example (tax on a purchase): A laptop costs £349.99 before tax and the rate is 12%. Open Add X% to Y, set X = 12 and Y = 349.99. The total is £391.9888 (round per your cash-register or invoicing rules).
For only the tax amount—not the total—use What is X% of Y? with the same numbers.
Calculations
Percentage increase or decrease
Example: What is the percentage increase from 16 to 25?
Equation: ((25 − 16) ÷ 16) × 100 = 56.25%
Steps
- 25 − 16 = 9 (difference between new and original)
- 9 ÷ 16 = 0.5625 (difference ÷ original value → relative change as a decimal)
- 0.5625 × 100 = 56.25% (multiply by 100 to express as a percent)
What is X% of Y?
Example: What is 20% of 250?
Equation: (20 ÷ 100) × 250 = 50
Steps
- 20 ÷ 100 = 0.2 (convert the percent to a decimal)
- 0.2 × 250 = 50 (multiply by the base amount Y)
X is what percent of Y?
Example: 30 is what percent of 125?
Equation: (30 ÷ 125) × 100 = 24%
Steps
- 30 ÷ 125 = 0.24 (part ÷ whole → ratio as a decimal)
- 0.24 × 100 = 24% (multiply by 100 for a percent; Y cannot be 0)
Add X% to Y
Example: Add 12.5% to 120
Equation: 120 + (120 × (12.5 ÷ 100)) = 135
Steps
- 12.5 ÷ 100 = 0.125 (percent as a decimal)
- 120 × 0.125 = 15 (increase = X% of Y)
- 120 + 15 = 135 (new total)
Subtract X% from Y
Example: Subtract 17.5% from 120
Equation: 120 − (120 × (17.5 ÷ 100)) = 99
Steps
- 17.5 ÷ 100 = 0.175 (percent as a decimal)
- 120 × 0.175 = 21 (discount amount = X% of Y)
- 120 − 21 = 99 (price after discount)
Frequently asked questions
- Which calculator should I use for sales tax on a price?
Use Add X% to Y with your pre-tax amount as Y and the tax rate as X to get the total. Use What is X% of Y? if you only need the tax amount.
- How do I calculate percentage increase or decrease between two numbers?
Use the Percentage increase or decrease form: From = original, To = new. Formula: ((new − old) ÷ old) × 100.
- How do I find what 15% of 200 is?
Use What is X% of Y? with X = 15 and Y = 200. Result: (15 ÷ 100) × 200 = 30.
- How do I calculate a percent discount off a price?
Use Subtract X% from Y: original price = Y, discount = X. That returns the sale price after one stated percent off.
- Which tool answers “X is what percent of Y?”
The X is what % of Y? section. It computes (X ÷ Y) × 100 (with Y ≠ 0).
- Is this site free?
Yes. All tools are free; no payment is required.
- Do I need an account?
No. Nothing here requires sign-up.
- Can I bookmark or share a single calculator?
Yes. Each tool has its own page in the header navigation (e.g. percentage change, percentage of a number)—use those URLs to bookmark or share.
A brief history of percentages
Percentages are everywhere in daily life—retail discounts, tax rates, interest, test scores, and data reporting. Expressing a number “per hundred” makes comparisons across different scales easy: a 5% rise means the same proportional idea whether you are talking about currency, population, or points on a test.
Antiquity and commerce. Roman finance used hundredths-style levies; for example, a 1/100 charge on auction sales (centesima rerum venalium) under Augustus. Thinking in parts of a hundred was already a practical way to standardize fees and shares.
Medieval and early modern Europe. As trade and banking grew, denominators of 100 became routine in arithmetic texts. By the late 15th and early 16th centuries, printed works used such methods for profit and loss, partnerships, and interest. By the 17th century, quoting rates in hundredths was familiar to merchants and lenders.
Why “percent”? The word comes from Latin per centum (“by the hundred”). Related forms appeared in Italian and other languages before settling into the modern sign %—a compact reminder that percentages are always anchored to one hundred as a reference whole.
Where “percent” means something slightly different
Sports: winning “percentage” as a decimal
In many sports leagues, a team’s record is reported as a decimal such as .500—meaning half of games won. Fans often call that a “winning percentage,” but the number is really a proportion (wins ÷ games played), not a value out of 100. A .500 record corresponds to 50% of games won, not 0.500%.
Road grades
Highway grade signs (e.g. 12% grade) describe slope: roughly speaking, vertical rise per horizontal run, scaled so that 100% would mean a 45° angle in the rise/run convention used for roads. That is geometry and safety engineering—not the same kind of “percent of a whole” as a tax rate, but the same per-hundred language reused for a different quantity.