Three things Indian finance code gets wrong (with the numbers)

I maintain a set of finance calculators for India. Every formula ships with a unit test, and the

build fails if a number drifts more than 0.5% from a verified value. That sounds like overkill for

arithmetic until you find out how much published finance code is quietly wrong.

Here are three errors I keep running into, with the actual figures. All three are asserted by tests

in — MIT, zero dependencies, 20 tests

Run the suite with npm test — plain node --test, no framework. The three traps above are in

there deliberately, so a regression that reintroduces one fails loudly.

If you have hit a fourth one, I would genuinely like to hear it.