I Built a Calculator App That Actually Feels Good to Use (And Runs Entirely in Your Browser)

Khader Vali — Sat, 04 Apr 2026 16:53:29 +0000

I built PercentMaster out of frustration with calculator sites that seem stuck in 2025 aesthetics, demand your email address to calculate a tip, or force you through three ad pages before giving you your result.

The simple tool I first created for managing my finances has evolved into an integral part of my daily routine, and I now want to introduce it to anyone who values great user experience design, privacy, and practical problem-solving without any BS.

PercentMaster is a completely free, no-registration-needed web application packed with more than 50 calculators and utilities that process on the client side, load instantly, and describe their purpose clearly.

Why I Built It

What sparked it was pure frustration. It was the feeling of opening up a calculator tool and being greeted with:

Bloated UI. Ads, pop-ups, and dark patterns everywhere.
Friction to use. Sign up, verify email, accept cookies, then calculate.
Privacy concerns. No visibility into whether your inputs were logged or sent somewhere.
Vague or missing explanations. You get a number back. Cool. But what does it mean? When should you actually use this?

I wanted to build the opposite: something fast, transparent, and respectful of your time and data.

What's Inside

Finance & Math

Percentage, discount, tip, and comparison calculators. The bread and butter.
Loan & mortgage calculators with amortization clarity.
Compound & simple interest. See how time and rates compound.
Income tax, sales tax, and salary estimators. Quick snapshots for your location/scenario.
Retirement & investment calculators. Rough projections to think about the long game.

Health & Education

BMI, calorie needs, and macro tracking tools.
GPA calculator. For students, parents, counselors.
Age calculator. Because you might want to know how many days old you are.

Developer & Utility Tools (The Fun Stuff)

Color converter. Hex, RGB, HSL, named colors—fast switching.
Password generator. Configurable length and character sets; no server involved.
Unit converter. Length, weight, volume, temperature.
Currency & crypto converter. Real-time rates (fetched client-side only).
Date calculator. Days between dates, add/subtract intervals.
QR code generator. Text to scannable code instantly.
Base64 encoder/decoder, JSON formatter/minifier, UUID v4 generator, Lorem ipsum generator. All the little things you Google for.
Image compressor. JPEG and WebP, runs entirely in your browser. No uploads to a server.

The utilities lean into privacy: if a tool doesn't need the internet, it doesn't touch it.

Tech Notes

Stack: React + TypeScript, built with Vite, styled with Tailwind CSS and accessible Radix UI primitives.

What mattered: Speed (everything loads in one bundle ~150KB gzipped), clarity (every calculator has a readable explanation or guide), and privacy (utilities that don't need a server run locally—no telemetry, no logs).

The Honest Bit

PercentMaster is not a substitute for professional advice. For tax liability, medical decisions, or legal questions, consult a qualified professional. This is a thinking tool, not a decision-maker.

How to Use It

Visit percentmaster, pick a calculator, and go. No account. No email. No "free trial" leading to a paywall.

The information for the blog can be used to figure out the exact formula used in the calculation of the calculators.

Try starting with:

The discount calculator if you want to feel good about your next purchase.
The compound interest calculator if you want a small dose of motivation to save.
The password generator if you've ever had to invent one by hand (we've all suffered).

What's Next

I'm always adding more tools based on what people ask for. If there's a calculator or utility you wish existed, let me know in the comments or reach out.

Thanks for stopping by. Hope it saves you some time.

Forem: Khader Vali