F.A.Q.

General

What does the `+` / `−` button do?

It toggles between additive and subtractive calculation mode.

Additive (+): After = Before + (Before × rate) — for VAT, GST, sales tax, tips, commissions.
Subtractive (−): After = Before − (Before × rate) — for Zakat, discounts, depreciation, deductions.

Toggle freely — the focused field stays put and the other two recalculate.

What is a “3-way” calculator?

It computes any of Before, After, or Amount when you enter one of them. “Three-way” refers to the three possible calculation directions: from Before, from After, or from Amount.

What is the difference between Before, After, and Amount?

Before — the starting amount (before applying the percentage)
After — the resulting amount (after applying the percentage)
Amount — the difference between Before and After

In additive mode: After = Before + Amount. In subtractive mode: After = Before − Amount.

Who is this calculator for?

Freelancers, small business owners, accountants, retailers, shoppers, travellers — anyone who needs to quickly calculate tax-inclusive or tax-exclusive amounts. Also useful for commission, tipping, Zakat, discounts, and margin calculations.

What does “flat rate” mean?

A single percentage applied to every calculation. Unlike tiered or progressive systems where different portions are taxed at different rates, the calculator uses one flat rate for simplicity and speed.

Rate

How do I set a rate above 40%?

Use the Custom Rate input in Settings. It accepts 0% to 1000% with two decimal places of precision. The quick popup on the calculator screen is limited to 0–40%.

How do I set a rate with finer granularity than 0.5%?

Use the Custom Rate input in Settings. For precise values like 12.37%, type directly into the field.

What happens if I set the rate to 0%?

At 0%, the direction does not matter:

Before = After always
Amount = 0 always
Nudge buttons are disabled
You cannot enter a non-zero Amount value

Useful for zero-rated goods, intra-company transfers, or any scenario where no tax applies.

Can I set a negative rate?

No. The minimum rate is 0%.

What is the maximum rate in subtractive mode?

99.99%. At 100% or higher, the After value would be zero or negative. If you switch to subtractive while the rate is above 99.99%, it is automatically clamped.

Nudge

Why does the Amount stay the same when I nudge?

The algorithm calculates a safe range (the “boundary”) around each value where the Amount does not change. Nudging moves within this range, letting you fine-tune to round numbers without changing the Amount.

What happens if I nudge beyond the boundary?

You cannot. The nudge buttons become disabled at the boundary. To go further, enter a new value manually — it will recalculate the Amount.

Why can’t I nudge the Amount field?

Amount is a derived value — always the difference between After and Before. If you need a specific Amount, tap the Amount field, enter the value, and the calculator works out the resulting Before and After.

Arithmetic

How is the % key different from the rate?

The % key has two modes:

Chain mode (after an operator): calculates a percentage of the first operand. Example: 100 + 10 % = gives 110.
Standalone mode (pressed directly): calculates the tax amount using the current flat rate. Example: with Gross = 100 and rate = 15%, pressing % gives 15.

Can I chain multiple operations?

Yes. Enter a value, press an operator, enter the next value, press another operator (this evaluates the first operation), and so on. Press = for the final result.

Keyboard

Keyboard shortcuts are not working. What should I do?

Ensure the calculator page has focus. Try a different browser (Chrome, Edge, Firefox, Safari are all supported). If using the embedded version on another site, the parent site may block keyboard events — try the standalone app instead.

Does keyboard input work on mobile?

Keyboard shortcuts are for desktop with a physical keyboard. On mobile, use the on-screen keypad.

Themes

Can I create my own theme?

Not currently. The five built-in themes cover a range of visual styles. If you have a specific theme request, submit it as a feature suggestion.

Does the theme affect battery life?

The Retro and Glassmorphism themes may use slightly more battery due to animation effects (scanline overlay, blur filter). Midnight Executive is the most battery-efficient on OLED screens.

Is my theme saved?

Yes. Your selected theme is saved to local storage and restored on your next visit.

Privacy and Data

Is any data sent to a server?

No calculation values, rates, or inputs are ever transmitted. All calculations happen entirely in your browser. Anonymous usage analytics (page views, error reports) may be collected to help improve the app. No personal information or calculation data is sent.

Are my calculations saved or stored?

No. The calculator does not store any calculation history. Everything is ephemeral — when you close the page or reload, all values are reset to zero.

Is the calculator open source?

No. The calculator is proprietary software with patents pending on the Three-Way Smart Round algorithm, the Dual-Bound Nudge feature, and the Input Anchoring method.

Technical

What platforms are supported?

Platform	Status
Web (all modern browsers)	✅ Available now
Installable web app (PWA)	✅ Available now
Android (via Capacitor)	✅ Available now
iOS / iPadOS	In development
Desktop (Tauri)	Planned
Browser extensions	Planned

Does it work offline?

The web version requires internet to load initially. Once loaded, all calculations work offline. The Android app works fully offline after installation.

What browsers are supported?

Chrome, Firefox, Safari, and Edge — the last two major versions of each. Older browsers may not display themes correctly.

How do I report a bug or suggest a feature?

Bug reports and feature suggestions are tracked in the project’s repository. Please include:

A clear description of the issue or suggestion
Steps to reproduce (for bugs)
Your browser and operating system

Known limitations

No calculation history

The calculator does not keep a history of previous calculations. Each calculation starts fresh. A calculation history feature is planned as part of a future premium offering.

No multi-currency support

By design, the calculator is currency-agnostic. It works with abstract amounts rather than specific currencies. You can set the decimal precision (0–3 places) to match your currency, but the calculator does not auto-detect currencies or apply currency-specific formatting.

No progressive or tiered rates

The calculator uses a single flat rate. It does not support progressive tax brackets or tiered rate structures.