Free Online Calculator – Percentages, Discounts, Tips & Everyday Math
The Rapid Tool Plus Online Calculator handles the math you actually search for: percentages, discounts, tips, and basic arithmetic — instantly, in your browser, with no app to install.
Keyboard works too — numbers, + − × ÷, Enter for =, Backspace to delete.
Skip to what you need
How to Use the Calculator
Enter your first number.
Choose an operation — +, −, ×, ÷, or %.
Enter your second number.
Press equals to get your result. Double-check the numbers you typed, especially decimals, before relying on the answer.
Percentage Calculator
Percentage questions are the single most common thing people search a calculator for — and they trip people up because "20% of 100" and "100 increased by 20%" are different questions with different answers. Here's how to tell them apart.
Example — what is 15% of 200?
(15 ÷ 100) × 200 = 30
Example — a price goes from 80 to 92:
((92 − 80) ÷ 80) × 100 = 15% increase
Example — 30 is 15% of what number?
30 ÷ (15 ÷ 100) = 200
Example — 45 out of 180:
(45 ÷ 180) × 100 = 25%
Discount Calculator
Working out a sale price is really two calculations chained together: find the discount amount, then subtract it.
Example — a $120 item at 25% off:
$120 × (1 − 0.25) = $90
Savings: $120 − $90 = $30
Tip Calculator
Common tipping ranges people search for
| Situation | Typical range |
|---|---|
| Sit-down restaurant | 18–22% |
| Counter service / fast casual | 10–15% |
| Delivery | 15–20% or $3–5 minimum |
| Rideshare / taxi | 15–20% |
| Hair salon / barber | 15–20% |
Basic Calculator
Straightforward arithmetic for everyday use:
| Operation | Example | Result |
|---|---|---|
| Addition | 125 + 75 | 200 |
| Subtraction | 500 − 175 | 325 |
| Multiplication | 25 × 8 | 200 |
| Division | 240 ÷ 8 | 30 |
Common Calculator Mistakes
- Mixing up "percent of" vs. "percent increase." These use different formulas — check which question you're actually answering before you type numbers in.
- Dropping a decimal. A misplaced decimal point (e.g., typing 1.5 instead of 15) silently produces a wrong-but-plausible-looking answer.
- Applying tax and discount in the wrong order. Most US retail applies sales tax after a discount, not before — check your receipt if the two orders give different totals.
- Not sanity-checking the result. If a 20% discount on a $50 item comes back as $200, something was entered backwards.
Frequently Asked Questions
What is 20% of 100?
20. Formula: (20 ÷ 100) × 100 = 20.
How do I calculate a discount percentage?
Subtract the sale price from the original price, divide by the original price, then multiply by 100: ((Original − Sale) ÷ Original) × 100.
How do you calculate percentage increase?
Subtract the old value from the new value, divide by the old value, and multiply by 100: ((New − Old) ÷ Old) × 100.
Is the Rapid Tool Plus calculator free?
Yes — the calculator is free to use directly in your browser, with no download or account required.
Can this calculator handle tax and tip together?
Yes. Add the tip percentage and tax percentage to the price separately (tip is typically calculated on the pre-tax amount), or use the percent function for each step in sequence.
Is a basic calculator enough for business or tax calculations?
For quick checks, yes. For binding financial, tax, or legal figures, verify with accounting software or a professional — a basic calculator doesn't account for jurisdiction-specific rules.
For financial, tax, legal, or medical decisions, verify important calculations using appropriate professional or authoritative resources.