About PercentBox

PercentBox is a free educational website that helps people solve everyday percentage and finance problems with transparent math. We combine instant calculators with written guides so you can both get an answer and understand the formula.

The project started because many online calculators bury simple tools under pop-ups, incomplete explanations, or results that hide how the number was produced. PercentBox keeps the interface light, mobile-first, and explicit: every major tool shows the formula, worked examples, and FAQ content you can read without an account.

What you can do here

• Core percentage math: what is X% of Y, reverse percentages, increase, decrease, and percentage change
• Shopping and dining: discounts, sale prices, and tips
• Business and study helpers: markup vs margin, VAT/tax add and extract, compound interest, and loan / EMI estimates
• Long-form guides that explain percentage points, stacked discounts, and more

How the calculators work

Calculations run entirely in your browser using standard arithmetic. There is no login wall and no server-side storage of the numbers you type. Optional history and theme preference stay in your device's localStorage so you can clear them anytime. Results update as you type so you can explore scenarios quickly.

Who it is for

• Students checking homework and exam-style percent problems
• Shoppers comparing discounts and sale prices
• Diners splitting tips and bills
• Freelancers and small businesses estimating markup, margin, or VAT
• Anyone who wants a reliable percent increase, change, or loan estimate without installing an app

Editorial standards

We write original explanations and examples. Tools are for education and everyday planning—not a substitute for professional tax, legal, or financial advice. When a calculation depends on local rules (for example VAT rates or loan products), we state that you should confirm figures with an official source.

The site may display ads to keep the tools free. Advertising partners may use cookies as described in our Privacy Policy. We also use analytics to understand which pages are helpful so we can improve them.

Sister project

If you need Portugal-specific salary estimates, see our sister site Portugal Net Pay / SalarioBox (English and Portuguese). PercentBox remains focused on general percentage and finance calculators.

Contact

Questions, corrections, or feedback: visit Contact or email hello@percentbox.com.

Start with the main percentage calculator or open a specialized tool below.