MyToolsBagMyToolsBag
All Tools

Roman Numerals Explained: Rules, Charts and Common Mistakes

·6 min read

Roman numerals use seven letters — I (1), V (5), X (10), L (50), C (100), D (500), M (1000) — and two rules that cover every valid numeral.

Rule 1: add when descending

Symbols written largest to smallest are added together. XVI is 10 + 5 + 1 = 16. MDCLXVI is 1666 and uses each symbol exactly once, in order.

Rule 2: subtract when a smaller symbol comes first

A smaller symbol immediately before a larger one is subtracted: IV is 4, IX is 9, XL is 40, XC is 90, CD is 400, CM is 900. Only I, X and C subtract, and only from the next two larger symbols. That is why 99 is XCIX and never IC.

Reading a long numeral

Scan left to right and chunk it: MCMXCIV is M (1000) + CM (900) + XC (90) + IV (4) = 1994. MMXXVI is 1000 + 1000 + 10 + 10 + 5 + 1 = 2026.

Years you will actually meet

  • 1776 — MDCCLXXVI
  • 1969 — MCMLXIX
  • 1999 — MCMXCIX
  • 2000 — MM
  • 2026 — MMXXVI

Common mistakes

Writing IIII for 4 (valid on some clock faces, not in standard notation), repeating V, L or D (never allowed), repeating any symbol more than three times, and stacking subtractions like IIX for 8 — it is VIII.

Why the limit is 3999

There is no standard symbol above M, so 3999 (MMMCMXCIX) is the ceiling. Larger values historically used an overbar to multiply by a thousand, which is not part of everyday usage. Check any numeral with the Roman Numeral Converter — it validates as you type.

Keep reading