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

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.