PuzzleDayTechniques for hard puzzles
Pencil marks
In hard grids you will run out of obvious moves early. Switch on Notes (press N) and write every candidate in each empty cell of a box or row. Placing a digit removes it from its neighbours’ notes automatically, so your marks stay up to date.
Naked and hidden pairs
Two cells in a unit that can only be the same two digits form a naked pair: no other cell in that unit can hold them. A hidden pair is the reverse — two digits that can only go in the same two cells of a unit, which means those cells can’t hold anything else.
Pointing
If, inside one box, a digit can only go in cells that line up in a single row, then that digit must be in that row within the box — so you can remove it from the rest of the row outside the box. The same works for columns.
Tips
- Turn off Show mistakes for a real test; turn it on while you are learning.
- Come back to the puzzle later: your progress and timer are saved, and fresh eyes often spot the next move.
- If you are stuck, look for cells with only two candidates — they are often the key.
More levels
Need a breather? Play the daily sudoku on medium. Want the ultimate test? Try expert sudoku.
Frequently asked questions
How hard is hard sudoku?
Hard puzzles start with about 27 clues. You will usually need notes and techniques such as pairs and pointing to make progress, but you never have to guess.
How long does a hard sudoku take?
Typically 15 to 40 minutes, depending on experience. Your best hint-free time is saved for each level.
Can I get a hint without spoiling the puzzle?
The Hint button fills in one cell — the one you have selected, or a random empty one. Use it sparingly: games with hints are not counted for best times.
Is there a daily hard sudoku?
Yes. Every level has its own daily puzzle and its own streak. Switch to Unlimited for more.