Killer Sudoku — Free Online Cage Puzzles

Killer Sudoku — Rules, Cage Tactics and a Free Online Daily Puzzle

Killer sudoku (also called sum sudoku, samunamupure or simply "killer") keeps every rule of ordinary sudoku and bolts arithmetic onto it. The 9×9 grid is still divided into rows, columns and 3×3 boxes that must hold 1–9 once each, but a dotted overlay cuts the grid into cages, and each cage carries a total: the digits inside it must add up to that number, and no digit may appear twice in the same cage. It is the most searched-for sudoku variant after the classic, and the reason is simple — it removes the free scanning that ordinary sudoku allows and replaces it with a genuinely different kind of deduction. This page gives you one date-seeded daily cage puzzle for everyone, unlimited Easy, Medium and Hard grids, and a killer sudoku calculator that lists every combination which can fill a cage of a given size and total.

Killer Sudoku Rules

• Sudoku rules still apply: each row, column and 3×3 box holds 1–9 exactly once.
• Cages: the coloured blocks outlined by dotted lines. The small number in the top-left corner of a cage is its total.
• Cage sum: the digits in the cage must add up to exactly that total.
• No repeats inside a cage: a cage may never contain the same digit twice, even when that is not otherwise forbidden.
• Unique solution: every board here is machine-verified to have exactly one solution under all of those rules combined.

A two-cell cage totalling 7 can only be {1,6}, {2,5} or {3,4} — and since the cells are in the same row, column or region, most of those options die almost immediately. That interplay is the whole game.

Killer Sudoku Calculator — Cage Combinations

The single most useful reference in killer sudoku is the list of digit combinations that can make a given total with a given number of cells. Choose a cage size and total below and the calculator prints every possibility. A cage that can only be one combination is a solved cage in disguise.

Quick facts worth memorising: a 3-cell cage totalling 24 must be {7,8,9}, and 6 must be {1,2,3}. A 4-cell cage totalling 10 must be {1,2,3,4}, and 30 must be {6,7,8,9}. A 5-cell cage totalling 15 is {1,2,3,4,5} and 35 is {5,6,7,8,9}. Two-cell cages 3 and 4 are forced to include the 1, and 16 and 17 are forced to include the 9.

The 45 Rule, With a Worked Example

Every row, column and 3×3 box in a killer grid contains the digits 1 through 9 exactly once, so every complete unit sums to 1+2+…+9 = 45. That single arithmetic fact unlocks deductions no amount of scanning can reach. Suppose the top row of your puzzle is partitioned into cages of sizes 3, 2 and 3 — nine cells covered by three cages — plus one leftover cell that belongs to a cage hanging down into the second row. Add the three fully-enclosed cage totals: say they are 12, 9 and 15, which sum to 36. The row must total 45, so the leftover cell — the outie — is 45 − 36 = 9. You have placed a 9 without touching a single candidate.

The mirror image works too. Imagine a 3×3 box containing cages that cover eight of its nine cells, with one cell of a neighbouring cage intruding — the innie. If the cages wholly inside the box total 38, the intruding cell must be 45 − 38 = 7, because the eight home cells plus the intruder still have to add up correctly against the box total. Beginners should practise this on paper with the calculator open: pick any row where the cages align obligingly, write the enclosed totals in the margin, subtract from 45, and pencil the answer lightly. After a dozen repetitions the pattern becomes visual — you will start seeing innies and outies the way chess players see forks.

Two cautions keep the rule honest. First, it applies only to true units — full rows, columns and boxes — never to arbitrary rectangles. Second, a cage that straddles the boundary counts for neither side until you account for exactly which of its cells lie inside. Mark boundary crossings with a dot before doing any arithmetic, and the rule will never mislead you. Combined with the combination table above, the 45 rule alone cracks the majority of easy and medium boards on this page.

Five Killer Sudoku Tips That Actually Work

1. Start with the small cages. Two-cell cages have at most four combinations, and a forced digit (a 1 in a total of 3, a 9 in a total of 17) immediately narrows its row, column and box. Solve every 2-cell cage you can before touching the big ones.
2. Learn the 45 rule. Every row, column and box sums to 45. If you can split a unit into cages plus one or two leftover cells (an innie or outie), the arithmetic tells you the leftover digits directly. This is the workhorse of hard killer puzzles, and it is worth practising on paper until it is automatic.
3. Watch for impossible combos. If a cage sits entirely inside one box and the box already contains a 7, then any combination containing a 7 is dead. Cross off combinations against the units the cage touches before you consider the rest of the grid.
4. Use the calculator as a checklist. When a cage has four or five combinations, write them all as pencil marks. As neighbouring cages place digits, combinations die one by one — that cascade is where most medium puzzles break open.
5. Never guess. Killer sudoku punishes guessing harder than classic sudoku because a wrong digit breaks a cage sum as well as a unit. If you stall, look again for a unit whose cages you can add up, or take one of the three hints.

Which Cages to Attack First — A Priority Order

Not all cages repay attention equally. Work them in this order and most puzzles open up within minutes:

1. Single-cell cages. A one-cell cage simply announces its digit — a free given. Place it immediately; it constrains a row, a column, a box and every neighbouring combination at once.
2. Two-cell cages with extreme totals. Totals 3, 4, 16 and 17 have only one or two combinations, and each forces a 1 or a 9 into the cage. Those forced extremes propagate further than any other early deduction.
3. Cages fully inside one box. Here ordinary sudoku logic multiplies the arithmetic: a combination digit that already appears elsewhere in the box dies instantly, often leaving a single survivor.
4. Units that almost partition into cages. Any row, column or box with exactly one innie or outie surrenders it to the 45 rule, as shown above.
5. Large cages last. Five-cell cages have sprawling combination lists that only become useful once neighbouring placements prune them. Leave them until the endgame, then read them as checklists.

This ordering mirrors how experienced solvers think: forced digits first, arithmetic structure second, exhaustive combination work last. Newcomers who want to drill the fundamentals on a smaller board should warm up with Mini Sudoku or the pure grid of classic Sudoku before returning to cages.

Difficulty Levels

Difficulty is set by how many givens survive and how the cages are shaped. Larger cages and fewer givens mean more arithmetic and longer chains.

• Easy: around 44 givens, mostly 2- and 3-cell cages. Finishable in about ten minutes with the small-cage tactics above.
• Medium: around 36 givens and the daily default. Needs the 45 rule and full combination elimination.
• Hard: around 30 givens with bigger cages. Expect real innie/outie work and twenty minutes or more.

A Short History of Killer Sudoku

Killer sudoku — samunamupure in Japanese, a blend of the English word "sum" and the Japanese word for number placement — emerged in Japanese puzzle magazines in the mid-1990s as editors searched for a successor to the classic grid. It reached British newspapers in 2005, where The Times christened it "Killer" for the way cage arithmetic assassinates casual scanning strategies, and from there it colonised puzzle books, airline magazines and eventually the browser. Its endurance is no accident: it is one of very few puzzles that fuse arithmetic fluency with pure deductive logic, rewarding both the accountant and the detective in the solver.

Champions of the variant emphasise its pedagogical side effect. Regular play drills mental addition of small distinct sets — partitioning totals like 23 into admissible triples becomes reflexive — which is why some primary schools use two-cell-cage killers as stealth arithmetic homework. Adults get a subtler benefit: the constant toggling between additive reasoning and positional elimination exercises cognitive flexibility, the same gear-shifting demanded by strategy titles elsewhere on this site, from 2048 to Minesweeper.

Purists debate etiquette questions to this day: is consulting a combination table "cheating", or is memorising the forty-odd forced totals simply part of mastery? Our position is pragmatic. Use the calculator freely while learning, memorise the extreme totals first, and let the middle of the table fade from crutch to confirmation as experience accumulates. Every daily board here is solvable with pencil, patience and the techniques on this page — no software required, no guesswork permitted.

Tournament culture has embraced the variant with particular enthusiasm. Championship rounds often feature a giant killer grid solved relay-style under a stopwatch, while fan newsletters circulate anthologies of notorious tournament grids as keepsakes. Rivalry between classic loyalists and killer devotees remains good-natured: both camps agree that a well-constructed puzzle, whatever its ruleset, delivers the same quiet euphoria when the final digit lands.

The Daily Puzzle and the Leaderboard

The Daily board is generated from a date-seeded deterministic generator, so every player on the same date receives exactly the same cages and givens — no refreshing until you like the look of the grid. Generate, verify uniqueness, and store: the whole construction happens in your browser in a couple of milliseconds, so nothing about your puzzle ever leaves your device. Finish it and your solve time joins the shared daily leaderboard Top 50, where a 🔥 streak tracks consecutive days.

If you want to keep solving after today's board, the Unlimited button produces an endless stream of fresh verified puzzles at any difficulty. Also worth a look: classic Sudoku for the pure grid, Jigsaw Sudoku for irregular regions, Sandwich Sudoku for outside-the-grid clues, and the Sudoku solver when you want to check a tricky position.

Is Killer Sudoku Free Here?

Yes — daily and unlimited play are both free, with no sign-up, no download and no external puzzle library. Tap a cell to select it, tap a digit on the pad to place, hold ✏️ Pencil to note candidates, and use the mistake counter and timer to keep yourself honest. The page loads on phones, tablets and desktops and runs on most school and work networks. When you want more number-grid variety, browse the number games and logic puzzles hubs.