Method
Roman notation combines I, V, X, L, C, D and M. A smaller symbol before a larger one subtracts only in standard pairs IV, IX, XL, XC, CD and CM.
Worked example
2026 = 2000 + 20 + 6 = MM + XX + VI = MMXXVI. XIV is 14 because X + IV = 10 + 4.
Assumptions and limits
This tool uses standard subtractive notation for 1–3,999. It rejects nonstandard forms such as IIX and XIIII. Historical inscriptions may use additive notation, which this converter does not accept.
Numbers above 3,999: the vinculum
Standard Roman numerals stop at MMMCMXCIX (3,999). For larger numbers, a historical convention called the vinculum draws a bar over a numeral to multiply it by 1,000: V̅ = 5,000, X̅ = 10,000, C̅ = 100,000 and M̅ = 1,000,000. It was used in the Middle Ages and later, but it is not a single fixed standard, and ancient Romans also wrote large numbers in other ways.
The converter bars the thousands and writes the remainder normally. 5,000 = V̅. 12,345 = 12 × 1,000 + 345 = X̅I̅I̅ + CCCXLV = X̅I̅I̅CCCXLV. The largest value it writes is 3,999,999 = M̅M̅M̅C̅M̅X̅C̅I̅X̅CMXCIX. To enter one in Roman-to-number mode, type the combining overline (U+0305) after each barred letter.
Roman numeral arithmetic
Roman numerals have no place value, so the calculator converts both numerals to ordinary numbers, calculates, and converts the answer back. XIV + IX = 14 + 9 = 23 = XXIII. Division gives a whole-number quotient and a remainder: XX ÷ III = VI remainder II.
Answers must stay between I (1) and MMMCMXCIX (3,999). Roman numerals have no zero or negative numbers, so X − X or a result above 3,999 is reported as out of range.
Dates in Roman numerals
Each part of a date is converted separately and joined with a separator. 25 September 2026 is IX.XXV.MMXXVI in US month-day-year order, or XXV.IX.MMXXVI in day-month-year order. Dots, middle dots, hyphens, slashes and spaces are all common; choose the order your readers expect.