How do I calculate the percentage of a number?

Divide the percentage by 100, then multiply by the number: 20% of 150 = 0.20 × 150 = 30. The X% of Y mode does exactly this and shows each step.

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

Divide the part by the whole and multiply by 100: 35 of 140 = (35 ÷ 140) × 100 = 25%.

What is the difference between percentage increase and decrease?

Only the sign. Both use (new − old) ÷ old × 100; a positive result is an increase, a negative one a decrease.

What about zero or negative baselines?

A zero whole is undefined (nothing can be a percent of zero) and the tool says so. Negative baselines can be computed, but interpret with care — the sign flips the meaning.

Percentage change vs. percentage points?

Change is relative to the baseline (4%→5% is +25%); points are the plain difference (+1 point). The note above works an example.

Does the order of X and Y matter?

Yes — in the change mode, X is the starting value and Y the new one. Swapping them converts an increase into the corresponding decrease.

Percentage Calculator | Online Calculators Free

What is a percentage calculator?

A percentage expresses a part of a whole per hundred. This tool covers the three questions people actually ask: a share of an amount (a tip, a discount, a tax rate), a part as a percent of a whole (what percent of the class passed), and relative change (how much the price or the balance moved).

The three formulas

Share: part = X% × Y, computed as (X ÷ 100) × Y.
Rate: percent = (X ÷ Y) × 100.
Change: percent change = ((new − old) ÷ old) × 100 — negative results are decreases.

Percentage points vs. percent

If an interest rate rises from 4% to 5%, that is one percentage point, but a 25% increase relative to the old rate. Headlines mix the two constantly; check which one the speaker means.

Worked example

A dinner costs $84.00 and you want to tip 15%.
Choose X% of Y, enter X = 15, Y = 84.
The board shows 12.6 — a $12.60 tip.
The formula line reads: 15 ÷ 100 × 84 = 12.60.

How to use it

Pick the mode that matches your question.
Type the two numbers; the result updates as you type.
Check the formula line to see the exact arithmetic.
Copy the result, print the sheet, or share a link that reproduces it.