Three Percentage Problems, One Tool
There are really only three percentage questions anyone ever asks. What’s 15% of 200? (30.) If I scored 37 out of 45, what percentage is that? (82.2%.) Revenue went from $840,000 to $920,000, what’s the percent increase? (9.5%.)
This calculator handles all three. Pick your mode, plug in the numbers, get the answer. It updates as you type, no button-clicking required.
How People Actually Use Percentages
Shopping math. The jacket is $180 and the store says 35% off. You could stand there doing mental math, or you could know instantly that’s $63 off, making the price $117. (Whether you should buy a $117 jacket is a different question.)
Grades. You got 42 out of 50 on the exam. That’s… let me check… 84%. Some people can do this in their heads, most people can’t when the numbers aren’t round. No judgment.
Business reports. Q3 revenue was $1.2M, Q4 was $1.35M. What’s the percentage change? It’s a 12.5% increase. The formula is ((New - Old) / |Old|) x 100, but honestly, who wants to remember that when they’re putting together slides at 11pm?
Sales tax. The bill is $47.50 and tax is 8.25%. That’s $3.92 in tax, totaling $51.42. In states with weird tax rates (looking at you, 6.625%), this saves a few seconds of mental gymnastics.
The Reverse Percentage Trick
The second mode, “X is what % of Y?”, is the one people forget exists. You know that 15 people out of a team of 64 volunteered for the committee. What percentage is that? 23.4%. Useful for reports, presentations, and anytime someone asks “what fraction of…” and wants a percentage answer.
For splitting restaurant bills specifically, the Tip Calculator is purpose-built for that. The Scientific Calculator is there when you need trig, logarithms, or more complex expressions. All calculations stay in your browser.