Read the numeral in groups
The symbols are I = 1, V = 5, X = 10, L = 50, C = 100, D = 500, and M = 1,000. Most groups add together. In the standard subtractive pairs IV, IX, XL, XC, CD, and CM, the smaller symbol subtracts from the larger one.
2026 becomes MMXXVI: M + M + X + X + V + I = 2,026. XLII reads as XL + I + I = 40 + 1 + 1 = 42. The result shows these groups for either conversion direction.
Why the range stops at 3,999
Larger values can be written using extended conventions such as overlines, but those require additional rules. This converter stays with the common seven-symbol form so the result has one predictable representation.
Invalid ordering is rejected rather than guessed. For example, IC is not accepted as 99; use XCIX. When reading an old inscription or clock face, keep its historical convention in mind.