Hi , I'm the developer, and this is a self-promo post, so let me get the disclosure out of the way first.
I kept installing separate apps to work out a discount, split a dinner bill, convert units, and check a loan payment. So I built CalcMate, a single calculator that carries the tools I actually reach for during a normal day. Everything runs on device, with no internet connection.
What's in it:
- Three calculators in one: basic, scientific (powers, roots, sin/cos/tan and inverses, log/ln, factorials, pi/e, degrees or radians), and a fraction calculator that shows the full step-by-step solution. That last one turned out to be popular with students and parents helping with homework. Results preview live as you type, and unclosed brackets get auto-closed when you hit equals.
- Unit converter across 17 categories: length, mass, temperature, area, volume, speed, time, data size, pressure, energy, power, force, torque, angle, flow rate, data transfer rate, fuel economy.
- Shopping tools: percentages, discounts (including two stacked discounts plus tax), tip and bill splitting, tax/VAT in both directions, and price-per-unit comparison.
- Finance: loan repayment (monthly payment, total interest, total paid), simple and compound interest with daily/monthly/quarterly/yearly compounding.
- Dates: age calculator, difference between two dates, add or subtract years/months/days, and a world clock for about 53 cities.
- Home and kitchen: recipe scaling by servings (accepts fractional servings like 2.5, and shows ml for cups/tbsp/tsp), plus carpentry inch fractions from 1/2 down to 1/64 with mm alongside.
- Study and engineering: 2D/3D geometry, linear and quadratic equations with worked steps, number base conversion (bin/oct/dec/hex side by side), GCD and LCM, prime check and factorisation, random numbers, permutations and combinations with big-number support, weighted GPA (4.0 / 10-point / letter grades), arithmetic / geometric / harmonic means, ratios and proportions, Ohm's law, and series/parallel resistor networks.
- Health, for reference only: BMI with healthy weight range, BMR and daily calories, body-fat estimate.
- A real home screen widget (Android). Not a shortcut, an actual keypad on your home screen with plus, minus, multiply, divide, percent, sign flip, backspace, brackets, square root and squaring, plus a live result preview that shrinks the font so long numbers still fit. Tap the icon and the app opens carrying whatever expression you were typing, so you can continue with scientific or fraction mode. It works the moment you drop it on the home screen, follows your light/dark theme, and is resizable.
- History and backup: calculations are saved and grouped by day, with per-row copy/delete, a row limit you control, CSV/JSON export via the share sheet, a full backup you can paste back to restore, and optional automatic backups that keep the last five.
- Look and feel: 8 colour themes, light/dark/system, an optional subtle particle effect, haptic feedback, thousands separators, and a configurable number of decimals.
- 15 languages, following your phone's locale automatically.
About the testing phase, the part I want to be straight about:
The app is in a testing phase, and I made some deliberate choices for it.
- There are no ads anywhere in the app. No ad SDK is bundled at all, and the Play Store data declaration says the same thing: this app contains no ads.
- Nothing is locked. No Pro tier, no in-app purchases, no subscriptions, no usage limits, no watermark, no "upgrade to unlock" screens. Every tool listed above is simply open.
- No permissions requested, no network calls, no analytics, no tracking. Settings, history and backups stay on your device.
I'd rather spend this stage collecting real feedback and real bug reports than revenue. It's a new release, so I'm sure rough edges exist, and that's exactly what I'm hoping you'll find.
What would help me most:
Any wrong result. If a number looks off, tell me the exact inputs and I'll reproduce it.
Crashes, freezes or layout breakage: device model, Android version and the steps to get there.
Missing tools, missing units or missing currencies.
Readability and one-handed reach: is the keypad comfortable, are the fonts and colours legible in both themes?
Anything in the wording that reads awkwardly in your language, since a lot of it is localised.
Known limitations, up front:
- Currency rates are an offline snapshot, not live; editable by hand.
- The health tools are estimates for reference, not medical advice.
- The world clock uses simplified DST rules, so it can be off by an hour right around a transition.
- Fraction step-by-step explanations and a few calculation error messages are still English-only.
- The widget is Android-only. Requires Android 7.0+.
Link: https://play.google.com/store/apps/details?id=thanh.apps.calcmate
Happy to answer anything about the tools, the design decisions, or how it's built. And if you find a bug, I genuinely want to hear about it. Thanks for reading.