Percentage Calculator: 3-in-1 Math Tool
Percentages can be confusing because the math changes depending on what you are trying to find. Are you looking for a discount? A grade? Or measuring growth?
The Countimator Percentage Tool splits these problems into three distinct calculators so you never use the wrong formula. Calculate Parts, Totals, and Percentage Change (Increase/Decrease) instantly.
Which Calculator Should You Use?
1. Find the Value (X% of Y)
"What is 20% of 150?"
Use this to calculate tips, sales tax, or discounts.
Formula: (Percentage ÷ 100) × Total
2. Find the Percentage (Part of Whole)
"25 is what percent of 100?"
Use this for test scores (e.g., getting 45/50 on a quiz).
Formula: (Part ÷ Whole) × 100
3. Percentage Change (Increase / Decrease)
"My rent went from $1,000 to $1,200. How much did it go up?"
This is the most complex calculation. It measures the Delta (difference) between an Old Value and a New Value.
- Positive Result (+): It is a Percentage Increase (Growth).
- Negative Result (-): It is a Percentage Decrease (Loss).
Formula: ((New Value - Old Value) ÷ |Old Value|) × 100
Common Percentage Examples
| Scenario | Which Tool? | Example Math |
|---|---|---|
| Leaving a Tip | Percentage of Total | 20% of $50 bill = $10 tip. |
| Test Grade | Part of Whole | 42 correct answers out of 50 = 84%. |
| Salary Raise | Percentage Change | $50k to $55k = 10% Increase. |
| Store Discount | Percentage of Total | 30% off a $100 jacket = You save $30. |
| Stock Loss | Percentage Change | Stock drops from $100 to $80 = -20% Decrease. |
Frequently Asked Questions
Move the decimal point of your bill one place to the left to find 10%. Then double that number.
Example ($45 bill): 10% is 4.5. Double it to get 9. Your 20% tip is $9.
Subtract the original number from the new number. Divide that difference by the original number. Finally, multiply by 100.
Formula: (New - Old) / Old * 100.
Yes! If a value doubles, it has increased by 100%. If it triples, it has increased by 200%.
However, a percentage decrease cannot exceed 100% (because you cannot lose more than you started with, unless going into debt).
Percentage Change implies time (Old vs. New value).
Percentage Difference compares two things that are equal in time (e.g., the difference in height between two people).
This tool calculates Percentage Change.
Note: All calculations are rounded to 2 decimal places for clarity. The "Percentage Change" tool handles negative values (decreases) automatically by displaying a minus sign (-).