JavaScript's IEEE 754 floating point format means 0.1 + 0.2 !== 0.3 — and that's just the obvious case. This post covers why it happens, where it silently breaks production code, and four concrete strategies: toFixed for display, integer arithmetic for money, a scale-round-ceil pattern for computed floats, and decimal.js for complex chains.

Sergio Lema

JavaScript uses IEEE 754 double-precision floating point for all numbers, meaning decimals like 0.1 + 0.2 can't be represented exactly in binary. This causes subtle bugs in financial and precision-sensitive code — not just the obvious 0.1 + 0.2 case, but composed calculations like Math.ceil(1.7000000000000002 * 100) / 100 producing 1.71 instead of 1.70. Four practical solutions are covered: using toFixed() only for display output, working in integer cents for monetary values, a scale-round-ceil pattern to neutralize floating point noise in pre-computed floats, and using decimal.js or big.js for complex chained financial calculations. The recommended default for money is integer arithmetic.

Why JavaScript Floating Point Math Breaks Your App (And How to Fix It)

Solution 1: toFixed() for Display, Not Logic

Solution 2: Integer Arithmetic (Work in Cents)

Solution 3: Scale Up, Round Out the Noise, Then Ceiling

Solution 4: decimal.js or big.js for Complex Use Cases