CoursePython from Scratch to Intermediate · Module 11: Capstone · part 75 of 75
Part 75 · Module 11: Capstone

Incident: Two digits for a year

8 min read·14 Oct 2026
Module 11 · Incident file · About 30 minutes

What happened

two-digit years 75 means 1975 every year 19.. century assumed fixing, testing before the date 1 January 2000 00 reads as 1900
Y2K in order: years kept as two digits (blue) with the century assumed (amber), fixed and tested (green) before 00 would read as 1900 (red).

For decades, many programs stored a year as two digits: 75 for 1975, 99 for 1999. Two digits were shorter to type, to print and to store, and every year began with 19, so the century seemed to go without saying.

It did not. On 1 January 2000 the two digits would be 00, and a program that added 1900 would read the year as 1900. This became known as the Year 2000 problem, or Y2K (K for a thousand). Large-scale fixing and testing of programs happened before 1 January 2000. This file keeps to those general facts: it quotes no figures and names no company.

"99" stored 1900 + 99 1999 right "00" stored 1900 + 00 1900 should be 2000
One rule, two answers: 1900 + 99 is right (green); 1900 + 00 gives 1900 when the year is 2000 (red).

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