What is Killer Sudoku?
Killer Sudoku is normal sudoku with a fun twist. The grid is broken into little dotted shapes called "cages", and each cage has a small number in the corner. That number is the target total. The digits you put inside the cage have to add up to it — and they all have to be different.
If you’ve already played our classic 9×9 sudoku, you already know most of the rules. Killer just adds the cages on top.
A typical Easy Killer puzzle has lots of small cages of two or three cells. The bigger you go in difficulty, the bigger the cages get and the fewer "given" numbers you start with. On Hard and Expert, the grid usually starts completely empty — you solve the entire puzzle just from the cage totals.
How is it different from regular sudoku?
You still need every row, every column and every 3×3 box to have the digits 1–9. But Killer Sudoku adds two new rules and usually starts with no numbers at all — just the cages and their totals.
- 🟦 Cells in the same cage must add up to the cage total
- 🔢 Numbers inside a cage must all be different
- 🔳 The cages have dotted edges so you can spot them
- 💡 Most puzzles start empty — you solve using totals alone
The 4 simple rules
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One of each in every row
Every row needs the digits 1 through 9 — no repeats.
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One of each in every column
Every column needs the digits 1 through 9 — no repeats.
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One of each in every box
Each 3×3 box needs the digits 1 through 9 — no repeats.
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Cage cells add up — and don’t repeat
Numbers inside a dotted cage must add to the cage total, and they all have to be different.
How to read a cage
Look for the small number in the top-left corner of a dotted box. That’s the cage total. The digits inside that cage must add up to it, and they all have to be different.
A cage with two cells and total 3 can only be 1+2. A cage with two cells and total 17 can only be 8+9. Tiny cages are your best friends — they have very few possible answers, and you can spot them in seconds.
Bigger cages have more options, but you can still narrow them down. A 3-cell cage with total 6 can only be 1+2+3 (any other combo would either repeat or go too high). Spotting these "single-combo" cages is the heart of Killer Sudoku.
Easy strategies for kids
- ✨ Tiny cages first — a 1-cell cage just IS the total
- ➕ Look for cages where only one combo works
- 📦 Use the "Box 45" trick: cages inside one 3×3 box must total 45
- ✏️ Tap Notes to write small candidate numbers in a cell
- 🔎 Tap Check to see if any answer is wrong so far
Most kids find that Killer Sudoku starts to feel natural after about five puzzles. If you’ve never played sudoku of any kind before, it can be worth doing a couple of Easy 9×9 sudoku puzzles first to get the row/column/box rule into your head. Once that’s second nature, the cages just feel like a fun extra layer on top.
Why kids love Killer Sudoku
- 🧠 Builds adding skills without it feeling like a maths sheet
- 🎨 The colourful cages make every puzzle look different
- 🕵️ Detective brain — follow the clues, find the answer
- ⏱️ Quick wins on Easy, longer challenges on Expert
- 📱 Works on phones, tablets, Chromebooks and laptops
Ready for more?
Once Easy Killer puzzles feel comfortable, try Medium Killer Sudoku. From there you can graduate to Hard Killer Sudoku, and finally take on Expert Killer Sudoku — our toughest cage puzzle.
Want a totally different brain workout? Switch back to classic 9×9 sudoku. Same logic, no adding. Younger players can also try our 4×4 sudoku and 6×6 sudoku starter grids.
Frequently asked questions
What age is Killer Sudoku good for?
Most kids enjoy Killer Sudoku from about 8 years old, once they’re comfortable adding to 20. Younger kids should start with our regular sudoku first, or try a 4×4 grid.
Do I need to be good at maths?
No — you only ever add small numbers (the biggest cage total in Easy is around 20). Most cages are just two or three cells, so it’s really easy adding.
Why is it called Killer Sudoku?
"Killer" just means "extra-tricky" — there’s nothing scary about the puzzle. Some sites call it Sumdoku, Addoku or Sum Sudoku because of all the adding.
Can I play without making an account?
Yes! Every game on this site is free with no signup, no email and no ads in the way of the puzzle.
Does it save my progress?
Yes — your puzzle, notes and timer save automatically in your browser. Close the tab and come back later, it’ll still be there.
How is Killer Sudoku different from classic sudoku?
It uses the same row/column/box rules but adds dotted cages with target sums. The cells in each cage must add to the target and all be different. That’s the only difference — but it changes the puzzle a lot.
Try other sudoku games
Different rules, same friendly board. Pick a sibling puzzle to play next.