The seven symbols
| Symbol | Value |
|---|---|
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1,000 |
The rules
Symbols are written from largest to smallest and added up: MDCLXVI = 1,000 + 500 + 100 + 50 + 10 + 5 + 1 = 1,666. Roman numerals use subtractive notation for 6 special cases where a smaller symbol precedes a larger one: IV (4), IX (9), XL (40), XC (90), CD (400) and CM (900). IV is used instead of IIII, and IX instead of VIIII, which avoids repeating a symbol more than 3 times.
Only I, X and C can be subtracted, and only from the next two larger symbols: 99 is XCIX, not IC. V, L and D are never repeated or subtracted. Without extra notation the largest number is 3,999 (MMMCMXCIX); larger numbers used a bar over a symbol to multiply it by 1,000.
Years in Roman numerals
| 1776 | MDCCLXXVI |
| 1900 | MCM |
| 1950 | MCML |
| 1990 | MCMXC |
| 2000 | MM |
| 2010 | MMX |
| 2020 | MMXX |
| 2025 | MMXXV |
| 2026 | MMXXVI |
| 2027 | MMXXVII |
History
Roman numerals grew out of Etruscan tally marks and remained the dominant numeral system in Europe well into the Middle Ages, until Hindu-Arabic numerals with a zero made arithmetic far easier. They are still used today for clock faces, book chapters, monarchs and popes, film copyright years, sporting events such as the Super Bowl, and outlines.