Roman Numerals Guide: Read Any Year

The seven symbols

A mnemonic for the order: "I Value Xylophones Like Cows Do Milk". The values alternate between 1 and 5 times a power of ten: 1, 5, 10, 50, 100, 500, 1000.

Rule 1: add from left to right

Symbols are written from largest to smallest and added: VI is 5 + 1 = 6, XII is 12, LXX is 70, MDCLX is 1000 + 500 + 100 + 50 + 10 = 1660. A symbol may be repeated up to three times in a row (III, XXX, CCC), but V, L and D are never repeated, because two of them would simply be the next symbol up.

Rule 2: a smaller symbol before a larger one subtracts

Because IIII is not used, 4 is written IV: one before five, meaning five minus one. The same idea gives IX (9), XL (40), XC (90), CD (400) and CM (900). Only these six subtractive pairs exist: I before V or X, X before L or C, C before D or M. You never write IL for 49 (it is XLIX) or VX for 5 (it is just V), and you never subtract more than one symbol at a time (IIX is not 8; VIII is).

Reading a long numeral: chunk it

Read from the left, taking the largest value you can at each step and checking whether the next symbol is bigger (a subtraction).

Another: MMXXIV. M, M = 2000; X, X = 20, total 2020; IV = 4, total 2024. And a trap: XCIX is 99 (XC = 90, IX = 9), not 100 or 101.

Writing a number: split it into thousands, hundreds, tens and units

Write each place separately, then join them:

• Thousands: 1 = M, 2 = MM, 3 = MMM.
• Hundreds: 1 = C, 2 = CC, 3 = CCC, 4 = CD, 5 = D, 6 = DC, 7 = DCC, 8 = DCCC, 9 = CM.
• Tens: 1 = X, 2 = XX, 3 = XXX, 4 = XL, 5 = L, 6 = LX, 7 = LXX, 8 = LXXX, 9 = XC.
• Units: 1 = I, 2 = II, 3 = III, 4 = IV, 5 = V, 6 = VI, 7 = VII, 8 = VIII, 9 = IX.

So 1987 is M (1000) + CM (900) + LXXX (80) + VII (7) = MCMLXXXVII. And 2049 is MM + XL + IX = MMXLIX. Numbers with 4s and 9s in them are the longest to write and the most common quiz questions.

Years you will meet

Film and television credits show the production year in Roman numerals, which is why MCMXCIX (1999) and MMXXIII (2023) look familiar. The 1900s all begin MCM; the 2000s begin MM. A year in the 1800s begins MDCCC; the 1700s MDCC; the 1600s MDC. Learning the century prefixes makes any year a two-step read.

Clock faces

Many clocks show 4 as IIII rather than IV. This is a tradition of clockmaking, not an error, and it has been explained in several ways (visual balance against VIII on the other side is the usual one). Quizzes ask about it occasionally; the answer is that IIII on a clock is the traditional exception.

Zero and big numbers

There is no Roman numeral for zero, and the system has no place value, which is why arithmetic in it is awkward. For numbers above 3999 the Romans used a bar over a numeral to multiply it by a thousand (V with a bar is 5000), but quizzes rarely go there.

Common mistakes

1. Writing IIII, XXXX or CCCC. Use IV, XL and CD.
2. Subtracting with the wrong pair. IL, IC and XD do not exist; 49 is XLIX, 99 is XCIX, 490 is CDXC.
3. Reading XCIX as 101. Small before big subtracts; chunk it as XC and IX.
4. Repeating V, L or D. VV is X, LL is C, DD is M.
5. Writing a year digit by digit. Split it by place value, not by its decimal digits as if they were separate numbers.

Glossary

• Additive notation: writing symbols largest to smallest and adding them.
• Subtractive pair: a smaller symbol before a larger one (IV, IX, XL, XC, CD, CM).
• Place value: the thousands, hundreds, tens and units a number splits into when you write it.
• Vinculum: the bar over a numeral that multiplies it by a thousand.