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Roman Numeral
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Sources & Methodology
Roman numeral conversion follows ISO 15924 standard notation rules. Subtractive pairs per classical Latin mathematical tradition verified against NCTM curriculum standards.
NCTM — Principles and Standards for School Mathematics
Mathematical curriculum reference used to verify the subtractive notation rules, symbol precedence, and conversion algorithms applied in this calculator.
Khan Academy — Roman Numerals Review
Reference for the seven Roman numeral symbols, additive and subtractive notation rules, and the constraint that no symbol may be repeated more than three times consecutively.
Number to Roman: Uses a greedy subtraction table of 13 values (M=1000, CM=900, D=500, CD=400, C=100, XC=90, L=50, XL=40, X=10, IX=9, V=5, IV=4, I=1). For each value, append the symbol as many times as it fits, subtract, move to the next smaller value.
Roman to Number: Parse left to right. If the current symbol value is less than the next symbol value (subtractive pair), subtract it. Otherwise add it. Sum all values.
Roman to Number: Parse left to right. If the current symbol value is less than the next symbol value (subtractive pair), subtract it. Otherwise add it. Sum all values.
⏱ Last reviewed: April 2026
How Roman Numerals Work — Complete Guide
Roman numerals are a numeral system that originated in ancient Rome and remained the standard way to write numbers in Europe well into the Late Middle Ages. They use seven letters from the Latin alphabet, each representing a specific value. Despite being largely replaced by Hindu-Arabic numerals for calculation, Roman numerals remain widely used in formal, ceremonial, and decorative contexts.
The 7 Basic Symbols
| Symbol | Value | Origin | Example Use |
|---|---|---|---|
| I | 1 | One finger / tally mark | I, II, III |
| V | 5 | Open hand (5 fingers) | V, VI, VII, VIII |
| X | 10 | Two hands crossed | X, XI, XIV, XIX |
| L | 50 | Half of C (100) | L, LI, LX, XC |
| C | 100 | Centum (Latin for 100) | C, CD, CM, CCC |
| D | 500 | Half of M (1000) | D, DC, DCC, CD |
| M | 1,000 | Mille (Latin for 1000) | M, MM, MMM, CM |
The 6 Subtractive Notation Pairs
IV = 4 IX = 9 XL = 40 XC = 90 CD = 400 CM = 900
Rule: Only I, X, and C may be placed before a larger value.
I precedes V (IV=4) and X (IX=9) only.
X precedes L (XL=40) and C (XC=90) only.
C precedes D (CD=400) and M (CM=900) only.
V, L, D are never used subtractively and are never repeated.
I precedes V (IV=4) and X (IX=9) only.
X precedes L (XL=40) and C (XC=90) only.
C precedes D (CD=400) and M (CM=900) only.
V, L, D are never used subtractively and are never repeated.
Repetition Rules
- I, X, C, M can be repeated up to 3 times consecutively (III=3, XXX=30, CCC=300, MMM=3000)
- V, L, D can never be repeated (no VV, LL, DD)
- To write 4, use IV (not IIII) — the subtractive rule overrides repetition
- IIII appears on some clock faces for tradition and aesthetic symmetry, but is non-standard
Common Year Conversions
| Year | Roman Numeral | Breakdown |
|---|---|---|
| 2026 | MMXXVI | MM=2000, XX=20, VI=6 |
| 2024 | MMXXIV | MM=2000, XX=20, IV=4 |
| 1999 | MCMXCIX | M=1000, CM=900, XC=90, IX=9 |
| 1776 | MDCCLXXVI | M=1000, D=500, CC=200, L=50, XX=20, VI=6 |
| 1900 | MCM | M=1000, CM=900 |
| 1066 | MLXVI | M=1000, L=50, X=10, VI=6 |
Roman numerals are still used today for movie copyright dates (filmed MMXXVI), Super Bowl numbering, Olympic Games editions, book front matter page numbering, clock faces, building cornerstones, and monarch/pope regnal numbers (e.g., King Charles III).
Frequently Asked Questions
Use the greedy subtraction method. Start with the largest Roman numeral value that fits (M=1000). Write that symbol, subtract its value, then repeat with the remainder. Work through all 13 values in order: M, CM, D, CD, C, XC, L, XL, X, IX, V, IV, I. Example: 2026 → MM (2000 left=26) → XX (6 left) → VI. Result: MMXXVI.
I=1, V=5, X=10, L=50, C=100, D=500, M=1000. Memory tip: I Value eXtremely Large Quantities of Materials. All other Roman numerals combine these seven symbols using additive notation (larger before smaller = add) and subtractive notation (smaller before larger = subtract, for 6 specific pairs only).
Six subtractive pairs exist: IV=4, IX=9, XL=40, XC=90, CD=400, CM=900. Only I, X, and C may precede a larger value, and only in these specific combinations. I can only precede V and X. X can only precede L and C. C can only precede D and M. V, L, and D are never used subtractively.
MMXXVI equals 2026 — the current year. Breakdown: MM=2000 (two thousands), XX=20 (two tens), VI=6 (five plus one). 2000+20+6=2026. You will see MMXXVI on film copyright notices, building dedications, and official documents dated this year.
MCMXCIX equals 1999. It is one of the most complex commonly used Roman numerals with four subtractive pairs. Breakdown: M=1000, CM=900, XC=90, IX=9. 1000+900+90+9=1999. Prince’s famous song “1999” would be titled “MCMXCIX” in Roman numerals.
The largest standard Roman numeral is 3,999 = MMMCMXCIX. You cannot write 4,000 in standard Roman numerals because MMMM (four Ms) violates the no-more-than-three rule and there is no symbol for 5,000 in standard notation. Extended systems use a vinculum (bar over a numeral) to multiply by 1,000, but this is non-standard.
No. The Roman numeral system has no concept of zero. The Romans used the Latin word “nulla” (meaning nothing) when they needed to express the absence of a quantity, but there was no symbol for it. This is one reason the Roman system was replaced by Hindu-Arabic numerals, which include zero and enable place-value arithmetic.
I, X, C, and M may each appear up to 3 times in a row (III=3, XXX=30, CCC=300, MMM=3000). V, L, and D may never be repeated — there is no VV, LL, or DD. If a value would require four repetitions (like 4 for I), use subtractive notation instead (IV=4, XL=40, CD=400).
Roman numeral clocks use I through XII (1 to 12). An interesting tradition: many clock faces use IIII instead of IV for 4. This is thought to be for visual balance (three symbols on that quarter of the face), historical preference, and to avoid confusion with the VI (6) across the dial. Despite being non-standard, IIII on clocks is widely accepted.
Roman numerals appear in: movie copyright dates (MMXXVI), Super Bowl numbering (Super Bowl LX), Olympic Games editions (Paris MMXXIV), book front matter (pages i, ii, iii), clock and watch faces, building cornerstones, monarch and pope names (King Charles III, Pope Francis I), and film sequels (Rocky II, Alien III).
2026 in Roman numerals is MMXXVI. Step by step: 2026 − 1000 = 1026 (write M). 1026 − 1000 = 26 (write M). 26 − 10 = 16 (write X). 16 − 10 = 6 (write X). 6 − 5 = 1 (write V). 1 − 1 = 0 (write I). Final: MMXXVI. Use the converter above to verify any year instantly.
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