Quick Percentage Calculator
Use these tools to solve the most common percentage problems for discounts, grades, budgeting, and growth rates.
1) What is P% of N?
2) A is what percent of B?
3) Percentage change from old value to new value
4) Apply a percentage increase or decrease
Why percentage skills matter
Percentages show up everywhere: store discounts, exam scores, taxes, interest rates, salary raises, and investment returns. A percentage calculator helps you avoid guesswork and make faster, better decisions with money and data.
At its core, a percentage is just a way to express part of something out of 100. That simple idea makes it easy to compare values of different sizes and track changes over time.
Core percentage formulas
1. Find a percentage of a number
Formula: Result = (P / 100) × N
- Example: 15% of 240 = (15/100) × 240 = 36
2. Find what percent one number is of another
Formula: Percent = (A / B) × 100
- Example: 45 is what percent of 60? (45/60) × 100 = 75%
3. Find percentage increase or decrease
Formula: Change % = ((New − Old) / Old) × 100
- Example: from 80 to 100 = ((100−80)/80) × 100 = 25% increase
Common real-life uses
Shopping discounts
If an item costs $120 and is 25% off, the discount is $30. Final price: $90.
Tips and tax
For a $48 restaurant bill, a 20% tip is $9.60. If sales tax is 8%, tax is $3.84.
Grades and test performance
If you score 42 out of 50, that is 84%. Percentages help compare scores across assignments with different point totals.
Budgeting and saving
If you save 10% of a $3,500 monthly income, you save $350 each month. Tracking percentages can make budgeting consistent and sustainable.
Percentage change: what to watch for
Percentage change uses the old value as the reference. This is important. Going from 50 to 75 is a 50% increase, but going from 75 back to 50 is a 33.33% decrease, not 50%.
- Increase when new value is greater than old value.
- Decrease when new value is lower than old value.
- If old value is 0, percentage change is undefined in standard math.
Quick mental shortcuts
- 10% is easy: move decimal one place left.
- 5% is half of 10%.
- 1% is 10% divided by 10.
- 15% = 10% + 5%.
- 25% = one quarter of the number.
- 50% = half of the number.
Common mistakes to avoid
- Confusing percentage points with percent change.
- Using the wrong base value in comparisons.
- Forgetting that 0.2 and 20% mean the same rate in different forms.
- Rounding too early in multi-step calculations.
Final thoughts
A good percentage calculator is more than a convenience tool—it is a practical decision aid. Whether you are evaluating a deal, checking performance, or planning financial goals, accurate percentage math helps you act with confidence.