How to calculate percentages: 8 everyday examples

To find a percentage of a number, divide the percentage by 100 and multiply: 20% of $85 is 0.20 × 85 = $17. To find what percent one number is of another, divide the part by the whole and multiply by 100 (42 out of 48 is 87.5%). To find a percentage change, divide the difference by the starting value and multiply by 100. Those three formulas cover almost every percentage problem in daily life.

“Percent” means per hundred. The National Institute of Standards and Technology puts it precisely: the % symbol simply stands for the number 0.01, so 20% is 20 × 0.01 = 0.2. Below are the formulas, some mental-math shortcuts, and eight everyday examples worked step by step with the same code as our percentage calculator.

The three formulas you need

The last two are shortcuts built from the first. Adding 7.25% is the same as multiplying by 1.0725, and removing it means dividing by 1.0725. Thinking in multipliers like this avoids most of the mistakes covered at the end of this guide.

Mental-math shortcuts

Most everyday percentages can be built from 10% and 1%. Using $64 as the example:

One more trick: X% of Y always equals Y% of X. 8% of 50 is awkward, but 50% of 8 is obviously 4, and so is the answer.

8 everyday examples

1. Tipping at a restaurant

Four friends get a bill for $86.40, which includes $6.40 of sales tax on $80 of food. They want to leave 20%.

• Tip on the pre-tax amount: $80.00 × 20 ÷ 100 = $16.00. Total $102.40, or $25.60 each.
• Tip on the full bill: $86.40 × 20 ÷ 100 = $17.28. Total $103.68, or $25.92 each.

Either approach is common; the difference here is $1.28. Before adding a tip, check whether the bill already includes an automatic gratuity. The IRS treats a charge the restaurant adds automatically, such as 18% for a large party, as a service charge, not a tip, because the customer did not choose the amount freely. The tip calculator handles pre-tax tipping, rounding and uneven splits.

2. Sales tax: adding it and removing it

US sales tax is set by states and local governments, so the combined rate depends on where you shop. Using an example rate of 7.25% on a $249.99 purchase:

• Tax: $249.99 × 0.0725 = $18.124275, which rounds to $18.12
• Total: $249.99 × 1.0725 = $268.114275, which rounds to $268.11

Going backward is where people slip. A receipt says $53.50 including 7% tax. The 7% was charged on the pre-tax price, so that price is 107% of itself on the receipt: $53.50 ÷ 1.07 = $50.00, and the tax was $3.50. Taking 7% of $53.50 ($3.745) and subtracting it gives $49.76, which is wrong. The sales tax calculator adds tax, works backward from a receipt total, or finds the rate that was charged.

3. Discounts and stacked coupons

A $120 jacket is 30% off, and you have a coupon for an extra 20% off at the register.

1. First discount: $120.00 × 30 ÷ 100 = $36.00 off, so $84.00
2. Extra 20% off the reduced price: $84.00 × 20 ÷ 100 = $16.80, so $67.20
3. Total saved: $120.00 − $67.20 = $52.80, which is 44%, not 50%

The second discount applies to a smaller price, so the combined discount is 1 − (0.70 × 0.80) = 0.44. The discount calculator works out stacked discounts and “buy one, get one” deals.

4. A pay raise, and whether it beats inflation

Your salary goes from $52,000 to $54,080. The raise is ($54,080 − $52,000) ÷ $52,000 = 0.04, or 4%.

Whether you are better off depends on prices. The Bureau of Labor Statistics measures US inflation with the Consumer Price Index. If prices rose 3% over the same year (an example figure), your real raise is 1.04 ÷ 1.03 − 1 = 0.97%, not 1% and not 4%. To see a raise as an hourly rate, use the salary calculator.

5. Test scores and grades

You answered 42 of 48 questions correctly: 42 ÷ 48 = 0.875, and 0.875 × 100 = 87.5%. When assignments carry different weights, a simple average is no longer right; the grade calculator handles weighted categories and tells you what you need on the final.

6. Up 25%, then down 20%: why equal percentages don’t cancel

A $80 item goes up 25% to $100 (80 × 1.25). Then it goes on sale at 20% off: $100 × 0.80 = $80, right back where it started. A 25% rise and a 20% fall cancel out because each percentage is taken of a different starting value. By the same logic, equal percentages do not cancel: $80 up 20% and then down 20% ends at $80 × 1.20 × 0.80 = $76.80.

The same asymmetry is why losses hurt more than gains. If an investment falls 50%, from $200 to $100, it needs a 100% gain to get back to $200.

7. Percent vs percentage points

Mortgage rates rise from 6% to 7%. That is an increase of 1 percentage point, but a (7 − 6) ÷ 6 × 100 = 16.67% increase in the rate itself. The effect on the payment is different again. On a $300,000, 30-year loan the monthly principal and interest goes from $1,798.65 to $1,995.91, up $197.26 or 10.97%, and total interest over the full term goes from $347,514.57 to $418,526.69. Try it in the mortgage calculator.

When a headline says rates “rose 1%,” it usually means one percentage point. Being precise about which one you mean avoids a lot of confusion.

8. What share of your income goes to housing

Your rent is $1,650 and your monthly take-home pay is $5,200: 1,650 ÷ 5,200 × 100 = 31.73% of take-home pay.

Mortgage lenders measure housing against gross income instead, and the CFPB describes 28% of pre-tax income as a common rule of thumb for total housing costs. On a $75,000 salary, that is $75,000 ÷ 12 = $6,250 a month, and 28% of $6,250 is $1,750. Our guide how much house can I afford? turns that budget into a home price.

Common percentage mistakes

• Using the wrong base. Always ask “percent of what?” A tip on the pre-tax amount, a discount on the reduced price and a percentage change from the starting value all depend on picking the right base.
• Adding percentages that happen in sequence. Stacked discounts and back-to-back price changes multiply; they don’t add.
• Removing tax by subtracting a percentage of the total. Divide by 1 plus the rate instead.
• Mixing up percent and percentage points, especially with interest rates.
• Confusing percentage change with percentage difference. Compare prices of $4.29 and $5.49: the higher price is 27.97% more than the lower one, the lower price is 21.86% less than the higher one, and their percentage difference (compared with the average of the two) is 24.54%. All three are correct answers to different questions.

Percentages also sit behind most money decisions, from interest rates to loan terms. For the next step, see compound interest explained and 72-month vs 60-month car loans, or run any of the calculations above in the percentage calculator, which shows every step.