Letter Series Puzzles
A run of letters following a hidden rule, and a gap at the end. The trick that makes these easy is the same one every time: turn the letters into their alphabet positions first, and the pattern stops being a pattern and becomes arithmetic.
Also known as alphabet series, letter sequences and missing letter puzzles.
The Same Algebra Played On The Alphabet
A letter series hides an arithmetic rule inside the alphabet. Convert each letter to its position — A is 1, Z is 26 — and the letter series becomes a number series: constant steps, alternating steps, or a doubling. The alphabet is just a mask over arithmetic.
How To Solve Letter Series Puzzles
- Convert the letters to their alphabet positions.
- Find the number rule exactly as in a number series.
- Watch for the wrap past Z — it is a cycle, not a wall.
- Convert your answer back to a letter.
Convert to positions and the problem renames itself. Every letter series is a number series wearing letters, and the wrap past Z is arithmetic, not magic.
| Family | What it covers |
|---|---|
| Fixed steps | undefined |
| Widening gaps | undefined |
| Letter pairs | undefined |
| Both ends at once | undefined |
| Alternating steps | undefined |
| Backwards runs | undefined |
| Long jumps | undefined |
| Mixed rules | undefined |
Positions, Steps, Wraps
The explanations here show the position chain for every term — letter to number, rule applied, number back to letter. Once you have read two worked chains, the wrap past Z stops being a trap and becomes part of the rule.
Letter Series Puzzles Frequently Asked Questions
How do you solve letter series puzzles?
Convert the letters to their alphabet positions first — A is 1 through to Z at 26 — and then treat it as an ordinary number series. Take the differences between consecutive positions: if they are equal the rule is a fixed step, and if the differences themselves rise steadily the gap is widening. Work out the next position, then convert that number back into a letter.
What are the alphabet positions?
A is 1, B is 2 and so on to Z at 26. It is worth knowing a few anchor points by heart rather than counting from A every time: E is 5, J is 10, O is 15, T is 20 and Y is 25. From those, any letter is at most two steps away.
What kinds of rules appear in letter series?
Five cover nearly everything here: a fixed step forwards or backwards, a gap that widens by one each time, pairs of letters where each letter runs its own series, one letter walking forward from A while another walks backward from Z, and an alternating step that switches between two sizes.
Do letter series wrap around from Z back to A?
Some published series do, but none here. Wrapping makes two different readings fit the same run — "add four" and "add four with wrap" agree right up until they suddenly do not — which would leave a puzzle with two defensible answers. Every series on this page stays inside A to Z, so the rule is never ambiguous.
How do I get faster at these?
Learn the anchor letters so the conversion costs you nothing, and always write the differences down rather than holding them in your head. Those two habits between them account for most of the speed difference between people who find letter series easy and people who find them impossible.
Are letter series the same as number series?
Underneath, yes. A letter is its position in the alphabet, so a run that advances four letters is a run that adds four. Converting the letters to numbers is the whole technique, and it is why these feel easy once you stop staring at the letters themselves.
What is a letter series?
A run of letters that follows a rule based on their positions in the alphabet — A is 1, B is 2, and so on. Once you convert, "C, F, I, L" is just 3, 6, 9, 12, and the puzzle becomes ordinary arithmetic. Some series step two or three letters at a time, some alternate two patterns, and some move backwards through the alphabet.