Percentage Calculator Guide: Calculate Percentages, Discounts & Percentage Change
A percentage calculator solves common percent problems: percent of, what percent, and percent change. It avoids base mistakes and converts between fractions, decimals, and percentages.
What is Percentage Calculator?
The percentage calculator helps with discounts, taxes, tips, grade weights, and KPI changes. It supports reverse operations (finding the original before a markup/discount) and shows work to prevent errors.
How to Use the Percentage Calculator
- Choose a mode: percent of, what percent, or percent change.
- Enter values (base and percent, or part and whole).
- Calculate to see the result and the equation used.
- Reverse the operation when you need the original before an increase/discount.
- Toggle fraction/decimal display for learning.
Formulas & Methods
- Percent of:
value = base * (p/100) - What percent:
p = (part/whole) * 100 - Percent change:
p_change = ((new - old)/old) * 100(base = old) - Reverse increase:
original = final / (1 + p) - Reverse discount:
original = final / (1 - p)
Assumptions & limitations
- Always confirm the correct base. Percent change uses the old value as the base.
- For chained changes, multiply factors: e.g.,
+10% then -10% = 1.10 * 0.90 = 0.99→ net -1%.
Examples
Example A — Discount
$80 with 25% off -> 80 * (1 - 0.25) = $60.
Example B — What percent?
30 is what percent of 120 -> 30/120 * 100 = 25%.
Example C — Change
From 200 to 260 -> ((260 - 200)/200)*100 = 30% increase.
| Task | Inputs | Output | |---|---|---| | Sales tax | $75, 7.5% | $5.63 | | Tip | $64, 18% | $11.52 | | Grade weight | 92/100 | 92% |
Pro Tips & Best Practices
- Convert percentages to decimals before multiplying.
- Watch your base on change problems—using the wrong base is the #1 error.
- For multi-step changes, use factor multiplication, not simple addition of percents.
- Round money to cents; keep more precision in intermediate steps.
Related Calculators
FAQ
Q: How do I calculate a percentage of a number?
A: Multiply the number by the percent as a decimal: percent_of = base * (percent/100).
Q: How do I find what percent one number is of another?
A: Divide part by whole and multiply by 100: percent = (part/whole)*100.
Q: How do I compute percentage change?
A: Use ((new - old) / old) * 100%. The base is the original value.
Q: Why do my results look off?
A: Check whether you used the correct base and converted the percent to a decimal.
Q: How do I reverse a percentage increase/discount?
A: Divide by (1 + p) for increases or by (1 - p) for discounts to recover the original.
Call to Action
Pick your mode, enter the numbers, and get an instant, step-by-step percent solution—great for shopping, grades, and KPIs.