Percentage Calculator
Three common percent questions—tips, ratios, and change from an old value to a new one.
What is X% of Y?
Result: 30
X is what percent of Y?
Result: 25.0000%
Percent change from old to new
Change: +25.0000%
FAQ
Why can percent change explode when the old value is near zero?
Relative change divides by the baseline. If the baseline is tiny, the same absolute jump looks like a massive percentage swing—mathematically correct but misleading for business headlines. Report absolute deltas alongside percentages, or use a different baseline when crossing zero.
Does this handle compound or stacked percentages?
Each calculator block is independent: “X% of Y” is a single multiplication, not successive compounding. For year-over-year stacks or chained tax-on-tax, model the sequence explicitly in a spreadsheet—order of operations matters.
How should I round money or invoice lines?
Floating point in browsers inherits IEEE quirks; for currency, many teams round per line item or per tax bracket per local law. Use this tool for quick mental checks; push final cents into an accounting engine with decimal types.
What if someone enters negative numbers?
“Percent of” still multiplies signed values; “part is what percent of whole” rejects a zero whole but allows negative parts (interpret carefully). Percent change uses `abs(old)` in the denominator to avoid sign flips—verify against your finance team’s convention for losses.
Is this a substitute for statistical margin of error?
No. These are deterministic arithmetic helpers. Confidence intervals and sample percentages need statistical tooling, not a three-field form.
Why show four decimal places on some results?
Small ratios (conversion rates) need precision before marketing rounds them to one decimal. You can truncate for display, but copying raw avoids accumulated rounding errors in downstream slides.
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