Once the calculator is in view and focused, you can type directly using your top-row number keys or Numpad. Use +, -, *, and / for arithmetic operators, press Enter or = to evaluate the expression, Backspace to delete the last digit, and Escape (ESC) to clear the entire calculation.

The percentage key follows commercial desktop calculator logic: pressing % on a standalone number divides it by 100 (e.g., 15% = 0.15). In chained operations such as 1000 + 20%, it automatically computes 20% of the base value (200) and adds it to produce 1200, making tax markups and retail discounts effortless.

The C (Clear) button resets the entire calculation state, clearing both the current display and any stored operator or previous operand. The Backspace key only removes the last typed digit on the active screen, allowing you to fix a typo without restarting a long multi-step calculation.

Mathematically, dividing any number by zero is undefined; instead of crashing or displaying raw 'Infinity', the calculator enters a safe error state with a localized explanation and resets cleanly on your next keypress. Extremely large or small numbers are automatically formatted with high-precision grouping to prevent overflow.

All calculations are executed 100% locally inside your browser—none of your numbers or financial figures are ever transmitted to an external server. Completed calculations are stored strictly in your browser's local storage so you can review or copy recent results anytime.