Logic
Sudoku is pure constraint logic with no arithmetic. Kakuro adds sums and a second constraint. How the two differ, which is harder, and what each one exercises.
Put a Sudoku grid next to a Kakuro grid and they look related: numbers, boxes, a solution that is unique and reachable by logic. They are not related in the way they feel to solve. Sudoku never asks you to add anything. Kakuro is entirely about sums. That single difference changes the strategy, the difficulty curve and what you are actually exercising.
Sudoku. A 9 by 9 grid divided into nine boxes. Fill every cell with 1 to 9 so that each row, column and box contains each digit exactly once. One rule, applied three ways. No arithmetic appears anywhere.
Kakuro. A crossword shape where you fill white cells with digits 1 to 9. Each horizontal and vertical run has a clue giving the sum of that run, and no digit may repeat inside a run. So every entry must satisfy two things at once: the right total and no duplicates.
In Sudoku, a candidate is eliminated by something you can see: that digit already appears in the row, the column or the box. Solving is scanning and crossing out.
In Kakuro, a candidate is eliminated by something you must compute: this combination cannot reach the clue, or it would repeat a digit. You are holding sets of possibilities in your head rather than reading them off the grid. That is why Kakuro feels heavier even when the grid is smaller.
Sudoku asks what cannot go here. Kakuro asks what set of digits could possibly make this total, and then what cannot go here.
Kakuro looks intimidating until you learn that certain sums have exactly one possible set. These are the footholds, and memorising a handful turns the puzzle from search into deduction.
Start with the most constrained runs, then use intersections: a cell where an across run and a down run meet must satisfy both, so the answer is whatever survives in both sets. That intersection step is the heart of Kakuro, and it has no real equivalent in Sudoku.
Play MyRin brain games with no account, then take the full versions with 600 levels each on your phone.
Play the free browser gamesNeither is a shortcut to general intelligence, and claims that any puzzle makes you broadly smarter deserve scepticism. What does transfer reliably is skill at the puzzle itself and comfort with the kind of thinking it demands. If your aim is variety, alternate them: the modes are different enough that one stays fresh while the other is resting.
Start with Sudoku if you are new to logic puzzles. One rule, visible constraints, and a clear ladder of techniques from naked singles to cross hatching to box line reduction. Our approach is in the MyRin Sudoku guide, and what makes one puzzle harder than another is covered in Sudoku difficulty explained.
Move to Kakuro once Sudoku feels mechanical. The combination tables take an evening to learn and they convert the whole puzzle from guesswork into deduction. Start with the MyRin Kakuro guide.
If you enjoy either, the same Japanese publishing tradition produced Hashi and Nurikabe, both of which drop numbers almost entirely in favour of shape and connection logic. The history is in the Nikoli puzzle tradition, and the rules are in Hashi and Nurikabe.
MyRin includes Sudoku, Kakuro, Hashi and Nurikabe with 600 levels each across easy, medium and hard, free on iOS and Android, with the ebook The Mind Games of Japan included.
For most people yes, because Kakuro asks you to hold two constraints at once: the digits in a run must sum to the clue, and no digit may repeat within that run. Sudoku has only the no repeat rule. Kakuro also has a larger search space at the start, since a run can begin with many combinations.
No. The arithmetic never goes beyond adding single digits to a total under 45. What Kakuro rewards is recognising which combinations can produce a sum, which is memory and pattern recognition rather than calculation.
They exercise different things. Sudoku is sustained constraint elimination and visual scanning. Kakuro adds numerical working memory, because you carry candidate combinations in your head. Alternating between them trains a wider range than either alone.
Both were popularised by the Japanese publisher Nikoli, which gave Sudoku its modern name and rules in the 1980s. Kakuro has roots in an American cross sums puzzle from the 1950s that Nikoli refined and renamed.