A Calculator With Variables: Name a Number Once, Use It Everywhere

How it works

1. Define: type tax=0.0825 (or any name=expression — the right side is evaluated first, so rate=5/100 works too) and press equals.
2. Use: type 149.99*tax in any panel — basic, scientific, or programmer. Variables resolve inside larger expressions, with parentheses, exactly as you'd expect.
3. Keep: variables persist between sessions. Close the app; tax is still there tomorrow.

You can also save any result directly as a variable from the result menu — no retyping.

What makes variables better than memory keys

• They have names. Six months later, mortgage_rate still explains itself; M2 never did.
• You can keep many. Each variable is independent — build up your own constants: kwh_price, overtime, g=9.81.
• They're global. Every panel shares the same variables, which turns 8 panels into one coherent workspace instead of 8 islands.
• They're safe. Reserved words (sin, pi, e, and other function names) can't be shadowed, so pi=3 is politely refused. Names can be up to 32 characters.

When variables are the wrong tool

They earn their place when a value is reused across several steps and might change — a tax rate, a unit price, an exchange rate you want to revise once and re-run everything against. For a value used once, naming it is pure overhead; just type the number.

They are also not a spreadsheet. There is no dependency graph recalculating everything automatically the moment a variable changes: expressions pick up the new value when they next evaluate, which means you stay in control of when a number moves, but it also means you should re-run the expressions that matter rather than assuming a figure on screen has caught up.

The rules, precisely

A variable is created either by assignment in the expression itself or by saving whatever is on the display to a name. Names are validated on entry, so a rejected name fails immediately rather than silently producing a wrong answer later — and an assignment left half-finished reports "Variable assignment is incomplete" instead of evaluating to something arbitrary.

Once a variable exists, referencing it inserts a token rather than pasting a snapshot of the number. That distinction is the whole point: change the variable and every expression referring to it uses the new value the next time it evaluates. A memory key cannot do that, because it stores a value with no name and no relationship to the expressions that used it.

Recipes

• Sales tax: tax=0.0825, then price checks become price*(1+tax) all day.
• Freelance quoting: rate=95, then rate*6.5 per line item, with the running total in a second panel.
• Physics homework: g=9.81, then 0.5*g*t^2 per problem, changing only t.
• Unit-adjacent math: convert once in the converter panel, save the result as meters, and reuse it in every follow-up calculation.

Variables store the value they had when defined — they're saved numbers, not live formulas — which keeps behavior predictable: changing tax later never silently rewrites an old calculation.

Frequently Asked Questions