The History of Kakuro: How Cross Sums Became a Japanese Icon

Kakuro feels unmistakably Japanese — the name, the elegant logic, the family resemblance to Sudoku. So it surprises most people to learn that the puzzle was actually born in the United States, under a completely different name, and only became "Kakuro" after crossing the Pacific. Its journey from a quiet American magazine feature to a global phenomenon runs through the same Japanese publisher that gave the world Sudoku, and it's a neat little story of how a puzzle can be invented in one place and made famous in another. Here's where Kakuro really came from. When you're done, you can play one yourself.

It started as "Cross Sums" in America

The puzzle we now call Kakuro first appeared in the United States in the 1960s, published in puzzle magazines under the plain-spoken English name "Cross Sums." The name said exactly what it was: a crossword-style grid where crossing runs of numbers had to add up to given sums.

Cross Sums is usually credited to a Canadian-born puzzle constructor named Jacob E. Funk, who created it for the American publisher Dell Magazines. It was conceived as a numerical cousin to the crossword — same satisfying interlocking grid, but powered by arithmetic and logic instead of vocabulary. For a couple of decades it lived a comfortable but unremarkable life in the back pages of puzzle digests, a favourite of math-minded solvers without ever becoming a household name.

Japan gave it a new name

The turning point came when the puzzle reached Japan. In 1980, the Japanese puzzle publisher Nikoli — a company that specialises in finding overlooked logic puzzles and perfecting them — picked up Cross Sums and gave it a Japanese name: "Kasan Kurosu" (加算クロス), which translates to "addition cross."

In classic fashion, that mouthful was soon contracted into something snappier. "Ka-san Ku-rosu" was shortened to "Kakuro," and the new name stuck. It's the same trick Japanese gave to many imported words, and it produced a name that travelled far better than the original. Nikoli refined the puzzle's presentation and conventions, and through the 1980s and 1990s Kakuro grew into one of the publisher's most beloved titles — second in popularity, for many Japanese solvers, only to a certain other number puzzle Nikoli was busy popularising at the same time.

That other puzzle was Sudoku

Here's the connection that explains everything. Nikoli is the same publisher that took an obscure American puzzle called "Number Place," renamed it Sudoku, and turned it into a Japanese sensation. So Kakuro and Sudoku grew up side by side in the same publishing house, shaped by the same editorial philosophy: pure logic, a single solution, no guessing, and elegant hand-made grids.

That shared heritage is why the two puzzles feel like siblings — because, in a sense, they are. If you've ever wondered how they stack up against each other, our Kakuro vs Sudoku comparison digs into the differences.

Riding the Sudoku wave to the world

For years, Kakuro stayed mostly within Japan. What changed everything was the global Sudoku explosion of the mid-2000s. When Sudoku swept through Western newspapers around 2004 and 2005, editors everywhere went looking for "the next Sudoku" to feed the sudden public appetite for logic puzzles — and Kakuro was the obvious candidate, already proven and waiting.

So Kakuro rode Sudoku's coattails into newspapers, puzzle books, and websites across the UK, the US, Europe, and beyond. The puzzle that had been quietly called "Cross Sums" for forty years suddenly had a catchy Japanese name and a worldwide audience. Today it's especially popular across Europe and Scandinavia, and it's a fixture of puzzle sites and apps everywhere.

Two names, one puzzle

The legacy of that transpacific journey is that Kakuro still answers to two names. Most of the world now says "Kakuro," but "Cross Sums" survives — especially in older American publications and among solvers who met the puzzle before its rebrand. They're completely interchangeable, as our explainer on what cross sums is lays out. It's a rare puzzle that carries its whole history in its names: the American original and the Japanese hit, side by side.

Not bad for a humble grid of numbers dreamed up in a 1960s puzzle magazine. The next chapter of Kakuro's history is the one you write every time you sit down with a grid. Play Kakuro now, or learn how to play if you're new to it.