Percentage Calculator (Percent of, Percent Change, Increase/Decrease)

This tool bundles four high intent percentage calculations in one place. Each tab is designed for a specific question:

1. X% of Y: find a portion of a value.
2. What percent is X of Y: turn a part and whole into a percent.
3. Percent change: measure increase or decrease between an original and new value.
4. Increase or decrease by percent: apply a percentage adjustment to a value.

These scenarios cover discounts, markup, grade changes, population growth, and many everyday calculations.

Results are estimates; rounding can affect totals.

The "X% of Y" calculation is the most common. The formula is straightforward:

• Formula: (X / 100) * Y

Example:

• 15% of 200 = (15 / 100) * 200 = 30

This is useful for tips, discounts, taxes, and any situation where you need to compute a portion of a total.

If you want to know how large a part is relative to the whole, use the "What percent is X of Y" tab.

• Formula: (X / Y) * 100

Example:

• 40 is what percent of 200?
• (40 / 200) * 100 = 20%

If the whole is zero, the percent is undefined. The tool shows a clear message in that case.

Percent change measures relative movement from an original value to a new value.

• Formula: ((new - original) / original) * 100

Example:

• Original = 80, New = 100
• Change = 20
• Percent change = (20 / 80) * 100 = 25% increase

A common mistake is to compare the difference to the new value instead of the original. Always divide by the original value to compute percent change.

If the original value is 0, percent change is undefined because division by zero is not allowed. In those cases, consider using absolute change instead of percent change.

Percent change and percentage points describe different things:

• Percent change is relative. It tells you how much something grew or shrank compared to its original value.
• Percentage points describe an absolute difference between two percentages.

Example:

• A rate moves from 10% to 12%.
• That is a 2 percentage point increase.
• The percent change is (12 - 10) / 10 = 20%.

Both are useful, but they answer different questions. Use percentage points when comparing rates, and percent change when comparing totals.

Discounts and sale prices

• Original price: 150
• Discount: 20%
• Discount amount: 150 * 0.20 = 30
• Sale price: 150 - 30 = 120

Tips and gratuity

• Bill total: 48
• Tip: 18%
• Tip amount: 48 * 0.18 = 8.64

Inflation over time

• Original price: 2.50
• New price: 3.10
• Percent change: ((3.10 - 2.50) / 2.50) * 100 = 24%

Grade changes

• Original score: 72
• New score: 84
• Percent change: ((84 - 72) / 72) * 100 = 16.67% increase

Salary increases

• Current salary: 62,000
• Raise: 5%
• New salary: 62,000 * 1.05 = 65,100

Use this calculator when you need a quick percent-of, percent change, or percent increase/decrease answer. It is helpful for pricing, reporting, discounts, and comparisons where relative change matters more than raw totals.