How to play Number Sums

Number Sums is a logic puzzle played on a square grid of digits from 1 to 9. Every row has a target number on its left, and every column has a target number above it. Your job is to decide which digits stay on the board and which ones go, so that the digits you keep in each row and each column add up exactly to its target. When every line adds up, the puzzle is solved.

You have two ways to mark a cell. Erase a digit when you are sure it does not belong, or circle it when you are sure it stays. Switch between the two modes with the tool buttons beside the board. Each wrong move costs one life, and you start each puzzle with three. Run out of lives and you can try the same board again from the start.

A simple way to begin

Start with lines where the choice is forced. If a row's target equals the sum of all its digits, every digit in that row stays. If a digit is larger than the target of its row or column, it can never be kept, so erase it. Small boards often open up from one or two of these easy lines, and each decision you make narrows the choices in the lines that cross it.

Next, look for combinations. If a row of five digits needs to make 7 and contains a 1, a 2, a 4, an 8 and a 9, only 1 + 2 + 4 can work, so the 8 and the 9 go. Checking a few combinations in your head is the heart of the game. When a line is complete, its target fades so you can see at a glance where work is left.

Colored regions

Hard and Expert boards add colored regions. Each region has its own small target in its corner, and the digits you keep inside it must add up to that number too. Regions give you extra clues, but they also mean every digit has to satisfy three sums at once: its row, its column and its region.

Difficulty levels

Easy boards are 5 by 5 and are the best place to learn the rules. Medium boards are 6 by 6 and need more combination work. Hard boards are 7 by 7 with colored regions, and Expert boards are 8 by 8 with long chains of reasoning. Every puzzle has exactly one solution, and you can always reach it by logic alone, without guessing.

Daily challenge

A new Daily Challenge appears every day. Everyone gets the same board, so you can compare times with friends. Come back each day to build your streak.

No ads, no sign-up

Number Sums is free to play in your browser on a computer, tablet or phone. There are no ads and no accounts. Your progress, your settings and your stats are saved in your own browser, so you can close the tab and pick up your puzzle later. If your eyes get tired, switch to the green eye-care background with one click at the top of the page.