How Roman numerals work
Roman numerals combine seven letters. You read a numeral left to right, adding values as you go — except where a smaller value sits before a larger one, in which case it is subtracted.
| Symbol | Value |
|---|---|
| I | 1 |
| V | 5 |
| X | 10 |
| L | 50 |
| C | 100 |
| D | 500 |
| M | 1,000 |
The subtractive rule
Only six subtractive pairs are valid in standard notation, and only powers of ten may be subtracted:
| Pair | Value | Why |
|---|---|---|
| IV | 4 | I before V |
| IX | 9 | I before X |
| XL | 40 | X before L |
| XC | 90 | X before C |
| CD | 400 | C before D |
| CM | 900 | C before M |
So 4 is IV, never IIII. 99 is XCIX — ninety plus nine — not IC, because I may only precede V and X.
Numbers above 3,999
Standard notation stops at MMMCMXCIX — 3,999 — because writing 4,000 would need four Ms in a row.
The classical extension is the vinculum: a bar over a numeral multiplies it by 1,000. So V̄ is 5,000 and X̄ is 10,000. This converter uses an overline for values above 3,999 and supports up to 3,999,999.
| Number | Roman |
|---|---|
| 4 | IV |
| 9 | IX |
| 40 | XL |
| 90 | XC |
| 400 | CD |
| 900 | CM |
| 1969 | MCMLXIX |
| 2000 | MM |
| 2026 | MMXXVI |
| 3999 | MMMCMXCIX |
Frequently asked questions
Why is 4 written IV and not IIII?
Standard notation uses the subtractive form, so IV is correct. IIII does appear historically, most famously on clock faces, where it balances the VIII opposite it visually.
Both were used in Roman times. IV became the standard through medieval scribal convention.
What is the largest Roman numeral?
In standard notation, MMMCMXCIX — 3,999. Beyond that a vinculum, or overline, is used to multiply by 1,000, extending the range to 3,999,999.
Why is there no zero in Roman numerals?
The system was designed for counting and recording quantities, not for positional arithmetic where a placeholder is needed. Romans used the word nulla when they needed to express nothing.
How do I write the current year in Roman numerals?
2026 is MMXXVI — two thousand (MM), twenty (XX), five (V), one (I). Enter any year above to check.