MyCalcToolkit
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Percentage Calculator

Calculate percentages in multiple modes: find X% of Y, percentage increase/decrease, what percent A is of B, and percentage difference between two values.

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Result

25% of 200 = 50

Formula

Result = (Percentage / 100) × Number

Step-by-Step

  1. 1Find 25% of 200
  2. 2Convert percentage to decimal: 25 / 100 = 0.25
  3. 3Multiply by the number: 0.25 × 200 = 50
  4. 4Answer: 25% of 200 is 50

How the Percentage Calculator Works

This calculator handles all common percentage operations. Each mode uses a different formula to give you the exact answer whether you're calculating discounts, tips, grades, or financial growth.

Core Percentage Formulas

X% of Y = Y × (X ÷ 100)

What % is A of B = (A ÷ B) × 100

% Increase = ((New - Old) ÷ Old) × 100

% Decrease = ((Old - New) ÷ Old) × 100

% Difference = |A - B| ÷ ((A + B) ÷ 2) × 100

Quick Examples

  • 15% of 240 = 240 × 0.15 = 36
  • 45 is what % of 180? = (45 ÷ 180) × 100 = 25%
  • From 80 to 100 = ((100 - 80) ÷ 80) × 100 = 25% increase
  • From 100 to 80 = ((100 - 80) ÷ 100) × 100 = 20% decrease

Common Uses for Percentage Calculations

  • Shopping discounts and sale prices
  • Tips at restaurants (15%, 18%, 20%)
  • Grade calculations and test scores
  • Investment returns and profit margins
  • Tax calculations and salary increases
  • Data analysis and statistics

How to Interpret Results

The percentage calculator gives you exact values — but context matters. A 20% discount on a $50 item saves $10, while a 20% raise on a $50,000 salary is $10,000. The same percentage applied to different base values produces vastly different practical outcomes. Always consider what the percentage is "of" when making decisions.

Practical Use Cases

  • Calculating sale prices and discounts while shopping
  • Determining tip amounts at restaurants (15%, 18%, 20%, 25%)
  • Computing grade percentages for assignments and exams
  • Figuring out tax amounts on purchases
  • Tracking portfolio returns (percentage gain/loss on investments)
  • Calculating markup and profit margins for business pricing

Worked Example: Calculating a Tip

Bill is $67.50, you want to leave 20% tip:

  • 20% of $67.50 = $67.50 × 0.20 = $13.50
  • Total with tip = $67.50 + $13.50 = $81.00
  • Quick mental math shortcut: 10% = $6.75, double it = $13.50

Common Mistakes

  • Confusing percentage increase with percentage points (going from 5% to 7% is a 2 percentage POINT increase, but a 40% percentage increase)
  • Applying percentage decrease and increase sequentially and expecting to return to original (100 - 20% = 80, then 80 + 20% = 96, NOT 100)
  • Reversing the base and result in "X is what percent of Y" (order matters: 30 is 60% of 50, not 50% of 30)
  • Using percentage difference when you mean percentage change (difference uses the average as base, change uses the original)
  • Forgetting to convert between percentage and decimal (7.5% = 0.075, not 7.5 in formulas)
  • Calculating compound percentages by adding (three 10% increases is not 30% — it's 33.1%)

Frequently Asked Questions

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

Use the formula: Percentage = (Part ÷ Whole) × 100. For example, 35 out of 200 = (35 ÷ 200) × 100 = 17.5%. This tells you that 35 is 17.5% of 200.

How do I calculate percentage increase or decrease?

Percentage change = ((New Value - Old Value) ÷ Old Value) × 100. If a stock goes from $50 to $65: ((65 - 50) ÷ 50) × 100 = 30% increase. If it drops to $40: ((40 - 50) ÷ 50) × 100 = - 20% decrease.

How do I reverse a percentage (find the original number)?

If you know the result after a percentage was applied, divide by (1 + rate) for increases or (1 - rate) for decreases. Example: A $72 item after 20% discount — original = $72 ÷ 0.80 = $90. After 15% tax added to get $115 — original = $115 ÷ 1.15 = $100.

What is percentage difference vs percentage change?

Percentage difference compares two values symmetrically: |A - B| ÷ ((A+B)/2) × 100. Percentage change compares to a reference value: (New - Old) ÷ Old × 100. Use difference when neither value is the "original" (comparing two cities); use change when tracking from a baseline (price over time).

How do I calculate X% of a number?

Multiply the number by the percentage and divide by 100. Example: 15% of 240 = 240 × 15 ÷ 100 = 36. Shortcut: move the decimal two places left (15% = 0.15), then multiply: 240 × 0.15 = 36.

How do percentages work with discounts and taxes?

For discounts: Final Price = Original × (1 - discount%). A $80 item at 25% off = $80 × 0.75 = $60. For tax: Final = Price × (1 + tax%). A $60 item with 8% tax = $60 × 1.08 = $64.80. Note: a 25% discount followed by 25% markup does NOT return to the original price.

Can I calculate percentage of a percentage?

Yes, multiply the percentages as decimals. 20% of 50% = 0.20 × 0.50 = 0.10 = 10%. This is useful for compound discounts: a 30% off sale with an additional 20% off the sale price = 0.70 × 0.80 = 0.56, meaning you pay 56% (total 44% off, not 50%).