Built a calculator that shows its work, not just the answer

Hey everyone! I've been working on Turborechner, a free online calculator hub, and wanted to share one of the tools: a percentage calculator.

Here's a weird thing — percentages are everywhere in daily life, but most of us just trust the number on the receipt/app without actually knowing how it's calculated. That 20% off tag, your loan's interest rate, the battery percentage on your phone, even your exam grade — it's all percentages, and yet almost nobody checks the math behind them.

So I built a calculator that doesn't just give you an answer — it shows the actual formula and step-by-step working behind every result.

It handles 7 different percentage problems in one tool:

- What is X% of Y?

- What percent is X of Y?

- X is Y% of what?

- Percentage increase / decrease

- Percentage change

- VAT calculation

Fun fact while building this: a LOT of people think adding 20% then subtracting 20% gets you back to the original number. It doesn't. €100 + 20% = €120, but €120 - 20% = €96, not €100. The base changes each time. That single misconception is probably costing people money on "discounts" they don't fully understand.

No sign-up, no account walls, works on mobile, and it's currency-independent so it works the same for EUR, USD, GBP, etc.

Link: https://turborechner.de/prozentrechner-standard

Would love any feedback, especially on what other calculation types would be useful to add!