20% of 80 is 16. Formula: 80 × (20 ÷ 100) = 80 × 0.20 = 16. To check: 10% of 80 is 8, so 20% is 8 × 2 = 16.

15% of 200 is 30. Formula: 200 × (15 ÷ 100) = 200 × 0.15 = 30. You can also calculate as 10% of 200 = 20, plus 5% of 200 = 10, total = 30.

How do I calculate percentage change?

Percentage change = ((New Value − Old Value) ÷ Old Value) × 100. Example: price changes from $50 to $65. Change = ((65 − 50) ÷ 50) × 100 = (15 ÷ 50) × 100 = 30% increase. If the result is negative, it is a decrease.

How do I calculate what percentage one number is of another?

Formula: (Part ÷ Whole) × 100. Example: 45 out of 60 on a test = (45 ÷ 60) × 100 = 75%. Example 2: 30 is what percent of 150? = (30 ÷ 150) × 100 = 20%.

How do I calculate percentage increase?

Percentage increase = ((New − Original) ÷ Original) × 100. To find the new value after an increase: New Value = Original × (1 + Rate ÷ 100). Example: $200 increased by 15% = 200 × 1.15 = $230.

What is the percentage difference between two numbers?

Percentage difference = (|Value1 − Value2| ÷ ((Value1 + Value2) ÷ 2)) × 100. Example: difference between 80 and 100 = (|80 − 100| ÷ ((80 + 100) ÷ 2)) × 100 = (20 ÷ 90) × 100 = 22.2%. Use this when neither value is the baseline.

Percentage Calculator 2026

Percentages are everywhere — exam scores, sale discounts, salary raises, bank interest, tax rates, tip calculations. But most people only know one or two types of percentage problems. This guide covers all six, with the exact formula and a worked example for each.

⚡ All 6 Percentage Formulas — Quick Reference

X% of YY × (X ÷ 100)

A is what % of B?(A ÷ B) × 100

Percentage change((New − Old) ÷ Old) × 100

Value after % increaseOriginal × (1 + Rate ÷ 100)

Value after % decreaseOriginal × (1 − Rate ÷ 100)

Find original (reverse %)Final ÷ (1 ± Rate ÷ 100)

Type 1 — What is X% of Y?

This is the most common percentage calculation. Used for tips, discounts, tax amounts, commission, and anything where you need a fraction of a number.

Result = Y × (X ÷ 100)

What is 20% of 80? → 80 × (20 ÷ 100) = 80 × 0.20 = 16
What is 7.5% tax on $1,200? → 1200 × 0.075 = $90
What is 18% tip on $85? → 85 × 0.18 = $15.30

✏️ Worked Example — 30% off a $350 jacket

1.Write the formula: Discount = 350 × (30 ÷ 100)

2.Calculate: 350 × 0.30 = 105

3.Subtract: $350 − $105 = $245

✓ You pay $245 after 30% off

Type 2 — What Percentage is A of B?

Use this when you have a part and a whole, and need the percentage. Common for exam scores, market share, completion rates, and nutrition labels.

Percentage = (A ÷ B) × 100

45 out of 60 on a test → (45 ÷ 60) × 100 = 75%
30 is what % of 150? → (30 ÷ 150) × 100 = 20%
Your team hit 320 of a 400 target → (320 ÷ 400) × 100 = 80%

✏️ Worked Example — What % is 12 of 48?

1.Divide the part by the whole: 12 ÷ 48 = 0.25

2.Multiply by 100: 0.25 × 100 = 25

✓ 12 is 25% of 48

Type 3 — Percentage Change

Percentage change tells you how much something increased or decreased compared to its original value. A positive result is an increase, a negative result is a decrease. Used for price changes, revenue growth, stock returns, and population data.

% Change = ((New Value − Old Value) ÷ Old Value) × 100

Price went from $50 to $65 → ((65 − 50) ÷ 50) × 100 = +30%
Stock dropped from $120 to $90 → ((90 − 120) ÷ 120) × 100 = −25%
Salary: $40K to $46K → ((46K − 40K) ÷ 40K) × 100 = +15%

✏️ Worked Example — House value change

1.House bought for $280,000. Now worth $336,000.

2.Change = 336,000 − 280,000 = 56,000

3.% Change = (56,000 ÷ 280,000) × 100 = 20

✓ House value increased by 20%

Common mistake: Percentage change is always relative to the original value, not the new one. A price going from $100 to $150 is a 50% increase. But going from $150 back to $100 is a 33.3% decrease — not 50% — because the starting point changed.

Type 4 — Percentage Increase

Use this when you know the original value and want to find the new value after applying a percentage increase. Common for salary raises, price markups, VAT/GST additions, and investment growth.

New Value = Original × (1 + Rate ÷ 100)

$200 increased by 15% → 200 × 1.15 = $230
$50,000 salary with 8% raise → 50,000 × 1.08 = $54,000
Price of $80 + 18% GST → 80 × 1.18 = $94.40

Type 5 — Percentage Decrease

The mirror of a percentage increase. Used for discounts, depreciation, markdowns, and any reduction. Instead of adding the percentage, you subtract it.

New Value = Original × (1 − Rate ÷ 100)

$350 jacket at 30% off → 350 × 0.70 = $245
$1,200 phone at 25% off → 1200 × 0.75 = $900
Car depreciated by 15% from $25,000 → 25,000 × 0.85 = $21,250

✏️ Worked Example — 40% off a $180 pair of shoes

1.Rate as decimal: 40 ÷ 100 = 0.40

2.Remaining fraction: 1 − 0.40 = 0.60

3.New price: 180 × 0.60 = 108

✓ Sale price is $108 (you save $72)

Type 6 — Reverse Percentage (Find the Original)

This is the trickiest one — you have the final value after a percentage was applied, and need to find the original before it was applied. Essential for accounting, tax calculations, and checking receipts.

If it was an increase: Original = Final ÷ (1 + Rate ÷ 100)
If it was a decrease: Original = Final ÷ (1 − Rate ÷ 100)

Price after 25% markup is $125 → 125 ÷ 1.25 = $100 original
Sale price after 20% off is $80 → 80 ÷ 0.80 = $100 original
Bill after 7.25% sales tax is $107.25 → 107.25 ÷ 1.0725 = $100 pre-tax

✏️ Worked Example — Find original salary before 10% raise

1.Current salary after 10% raise: $55,000

2.It was an increase, so: Original = 55,000 ÷ (1 + 10/100)

3.= 55,000 ÷ 1.10 = 50,000

✓ Original salary was $50,000

Why this trips people up: Many people assume if a price increased by 25%, you just subtract 25% to get back. Wrong. If $100 becomes $125 (up 25%), subtracting 25% from $125 gives $93.75 — not $100. Always divide by (1 + rate) to reverse an increase.

Mental Math Shortcuts for Percentages

You don't always need a calculator. These shortcuts let you estimate percentages in your head within seconds — useful for tips, discounts, and quick checks.

PercentageMental trickExample (on $80)

1%Move decimal 2 places left$0.80

5%Half of 10%$4.00

10%Move decimal 1 place left$8.00

15%10% + half of 10%$12.00

20%Double 10%$16.00

25%Divide by 4$20.00

33%Divide by 3 (approx)~$26.67

50%Divide by 2$40.00

75%Divide by 4, multiply by 3$60.00

Frequently Asked Questions

What is 20% of 80?+

20% of 80 is 16. Formula: 80 × (20 ÷ 100) = 80 × 0.20 = 16. Mental math shortcut: 10% of 80 = 8, double it = 16.

What is 15% of 200?+

15% of 200 is 30. Formula: 200 × 0.15 = 30. Mental math: 10% of 200 = 20, half of that (5%) = 10, add together = 30.

How do I calculate a percentage change?+

Formula: ((New Value − Old Value) ÷ Old Value) × 100. Example: price goes from $50 to $65. Change = ((65 − 50) ÷ 50) × 100 = (15 ÷ 50) × 100 = 30% increase. Negative result = decrease.

How do I find the original price before a percentage discount?+

Divide the sale price by (1 − discount rate). Example: item is $75 after a 25% discount. Original = $75 ÷ (1 − 0.25) = $75 ÷ 0.75 = $100. For a markup: divide by (1 + rate). Never just add the percentage back — that gives the wrong answer.

What is the difference between percentage change and percentage difference?+

Percentage change is used when one value is the baseline (before/after). Percentage difference is used when comparing two independent values with neither as the reference point. Formula for difference: |V1 − V2| ÷ ((V1 + V2) ÷ 2) × 100. Example: 80 vs 100 → |80-100| ÷ 90 × 100 = 22.2%.

How do I calculate a 20% tip quickly?+

Move the decimal left one place (that's 10%), then double it. Bill is $65: 10% = $6.50, double = $13.00 tip. For 15%: find 10% ($6.50), find 5% (half of $6.50 = $3.25), add together = $9.75.

What is 7.5% of 1200?+

7.5% of 1200 = 1200 × 0.075 = 90. You can also break it down: 5% of 1200 = 60, 2.5% of 1200 = 30, add together = 90.

This guide is for educational purposes. For business, accounting, or tax calculations always verify with a qualified professional.

Percentage Calculator — How to Calculate Percentages (All 6 Types Explained)