499 in Roman numerals

How CDXCIX is built

Roman numerals are written one decimal place at a time, largest first.

1. CDhundreds · 4C before D means 500 − 100 = 400. This saves writing CCCC.
2. XCtens · 9X before C means 100 − 10 = 90. This saves writing LXXXX.
3. IXones · 9I before X means 10 − 1 = 9. This saves writing VIIII.

400 + 90 + 9 = 499

The pairs CD and XC and IX use subtraction: a smaller letter before a larger one is taken away from it. Only six pairs work this way: IV, IX, XL, XC, CD and CM. More on subtraction

Mistakes to avoid

• Not ID. It looks like a shortcut, but I may only come before V or X, not D. The correct form is CDXCIX.
• Not CCCCLXXXXVIIII (14 letters). That adds everything up without subtraction. The Romans sometimes wrote numbers this way, and clocks still show 4 as IIII, but today CDXCIX (6 letters) is the standard.