Three Ways to Think About Percentages
"Percentage" questions usually come in one of three shapes, and each one uses a slightly different formula. This calculator covers all three so you don't have to remember which formula goes with which question — just pick the mode that matches what you're trying to find.
1. X% of Y (Finding a Portion)
This is the most common percentage question: "What is 15% of $200?" The formula is simply (X ÷ 100) × Y. It's useful for tips, discounts, sales tax, commissions, and figuring out a portion of any total — for example, how much a 20% down payment would be on a $300,000 home, or how much a 7% raise adds to your salary.
2. X Is What Percent of Y (Finding a Rate)
This mode answers "45 is what percent of 180?" using the formula (X ÷ Y) × 100. It's the formula behind things like test scores (points earned ÷ points possible), savings rates (amount saved ÷ income), and ownership stakes (shares you own ÷ total shares). The result tells you the relationship between the two numbers as a percentage.
3. Percentage Change (Increase or Decrease)
This mode answers "I went from 80 to 100 — what's the percentage change?" using the formula ((Y − X) ÷ X) × 100. A positive result means an increase; a negative result means a decrease. This is the formula behind year-over-year growth, price changes, weight loss/gain percentages, and comparing any "before" and "after" value. Note that percentage change is not symmetric — going from 80 to 100 is a 25% increase, but going from 100 back to 80 is only a 20% decrease.
A Quick Note on Rounding
Results are shown to two decimal places for precision, but in everyday use it's common to round percentages to the nearest whole number or tenth. For financial calculations — especially anything involving interest rates or tax — small rounding differences can compound over time, so it's worth keeping the extra decimal places when the stakes are higher (like comparing loan offers).