Three months is not ninety days

A rule about fixed-term contracts says three months. A programmer reads that as ninety days, and writes it in one line.

Three months is calendar months. Depending on where the contract starts, it is anywhere from 89 to 92 days, and the difference is a person’s legal standing.

The same project found the other half of this problem. The server clock runs on UTC. For two hours every night it is already tomorrow locally, and a rule that asks “is this contract over today” gives a different answer depending on when it is asked. Rules now take today as an argument, instead of looking it up.

Dates are where plain English and arithmetic part ways. It is always worth asking which one the law meant.