The 3 Golden Rules of Roman Numerals: Addition, Subtraction, and Repetition Made Easy

Roman Numerals are not just for old clocks and chapter headings they are a clever, logical system that has been used for thousands of years.

If you find Roman Numerals confusing, don’t worry. The entire system is built upon just three (3) simple rules. Once you understand these rules, you’ll be able to read and write any number, from 1 all the way up to 1000, easily.

The First Golden Rule: The Rule of Addition (Adding)

This is the most straightforward and simplest rule to follow.

What is the Rule?

When a smaller value symbol is placed to the right of a larger value symbol, you add the values together.

In Simple Terms: If a big number symbol comes first, and a smaller one follows, just add them up.

Roman Numeral	Breakdown	Total Value	How to Think About It
VI	V+I	5+1=6	V (5) is bigger than I (1). Since I is on the right, we add.
LX	L+X	50+10=60	L (50) is followed by X (10).
MCL	M+C+L	1000+100+50=1150	They go from large to small, so we add everything.
XXIII	X+X+I+I+I	10+10+1+1+1=23

The Second Golden Rule: The Rule of Subtraction (Subtracting)

This rule is a bit trickier, but it’s essential for writing numbers like 4, 9, 40, and 90.

What is the Rule?

When a smaller value symbol is placed to the left of a larger value symbol, you subtract the smaller value from the larger one.

Important Condition: This rule does not apply to all symbols. Only specific symbols can be used for subtraction, and only with specific numbers.

Which Symbols Can Subtract?

Only three symbols are allowed to be placed on the left to subtract:

1. I (1)
2. X (10)
3. C (100)

Roman Numeral	Breakdown	Total Value	How to Think About It
IV	V−I	5−1=4	The smaller symbol (I) is on the left of the larger symbol (V), so we subtract (5-1).
IX	X−I	10−1=9	The I (1) is on the left of the X (10).
XL	L−X	50−10=40	X (10) can only precede L (50) or C (100).
CM	M−C	1000−100=900	C (100) can only precede D (500) or M (1000).

Avoid Mistakes: You can never subtract V, L, or D (the symbols for 5, 50, and 500). Also, you can only subtract a number from the next two larger values (e.g., I can only subtract from V and X, not L).

The Third Golden Rule: The Rule of Repetition (Repeating)

This rule tells you how many times you are allowed to repeat a symbol next to itself.

What is the Rule?

No symbol should be repeated more than three (3) times in a row.

Which Symbols Can Repeat?

Only four symbols can be repeated:

1. I (1)
2. X (10)
3. C (100)
4. M (1000)

Roman Numeral	Breakdown	Total Value	What is NOT Allowed?
III	1+1+1	3	Repeating I three times is correct.
XXX	10+10+10	30	Repeating X three times is correct.
CCC	100+100+100	300	Repeating C three times is correct.
LXX	50+10+10	70	L is not repeated, we just used the Addition Rule here.

Which Symbols Cannot Repeat?

The symbols V (5), L (50), and D (500) are never repeated.

Why Not?

• VV is incorrect. You should use X (10) instead.
• LL is incorrect. You should use C (100) instead.
• DD is incorrect. You should use M (1000) instead.

Final Tip: Using the Rules Together

When you write a large number, you need to use all three rules together. Always start by breaking down the number from the largest place value (thousands, hundreds, tens, ones).

Example: How to Write 1994

1. 1000 = M
2. 900 = 1000−100 = CM (Subtraction Rule)
3. 90 = 100−10 = XC (Subtraction Rule)
4. 4 = 5−1 = IV (Subtraction Rule)

Add it all up: 1000+900+90+4 = MCMXCIV

Roman Numerals are not a confusing puzzle. By remembering these 3 Golden Rules, you can become an expert in this ancient writing system