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📖 How to Play Mad Add
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Mad Add is a numerical logic puzzle. You're given a grid full of single-digit numbers. On the right of every row sits a target sum for that row, and on the bottom of every column sits a target sum for that column. Your job is to delete the right numbers — and only the right numbers — so that what remains in every row, and every column, hits its target at the same time. There is no arithmetic; there's no rearranging. Just decide which numbers stay and which numbers go.
Each cell has three states. Tap an undecided cell once to delete it — a red ✕ appears and the number stops counting. Tap a second time to lock it as kept — a small green ✓ pins it in. Tap a third time to clear back to undecided. As soon as a row or column hits its target it turns green ✓. If it goes over the target, it pulses red — you've kept too much and need to delete more.
When you've locked enough cells in a row that their sum already equals the target, the target badge glows gold and starts to pulse. Tap the glowing badge and the rest of that row's undecided cells get auto-deleted in one step — a satisfying time-saver for the endgame. The same shortcut works for columns. It's an undoable action like any other.
Stuck? Hit the 💡 hint button. The first three hints are free — each reveals one correct cell. After that every hint adds +30 seconds to your timer, so you can keep going but it costs you a fast time. The little badge on the hint button always shows what's left or what the next one will cost.
Two independent dials let you tune the challenge. Pick a grid size from 5×5 up to 11×11, then set a difficulty from Beginner through Cyborg ☠. Every size offers all seven difficulties, so a quick 5×5 Beginner is a gentle warm-up and an 11×11 Cyborg is a serious workout. Harder difficulties demand more deletions to solve and at the top tiers the puzzle is verified to have exactly one valid solution — no guessing.
Play Mad Add free online — no download, no sign-up. Mad Add is a browser-based math puzzle game that runs on any device. Work through 7 difficulty levels across 7 grid sizes, take on the seeded daily challenge to grow your streak, and share your time to challenge friends with the same puzzle.
The daily challenge resets every midnight and is the same puzzle for every player worldwide on that date. Build a streak, beat your personal best across sizes, and use the challenge link to send any specific puzzle to a friend.
Boards are generated fresh so no two sessions repeat — the daily board is the deliberate exception, a single shared puzzle for every player in the world. Best scores stay in your browser, nothing is uploaded. Math Slide and Number Bonds work the neighbouring mental-math muscles.
Mad Add is my favourite kind of puzzle: one sentence of rules, and then the floor drops. You get a grid of digits, a target sum beside every row, a target sum beneath every column, and one power — delete. Cross out the right numbers and what remains hits every target simultaneously. No arithmetic tricks, no rearranging, nothing hidden up the sleeve. As a certain regional manager from The Office would put it, the whole game is addition through subtraction — and honestly, that line is half the reason the game exists in this form.
Under the hood, Mad Add put me through the same fight Kakuro did. Generating boards that are guaranteed solvable can send a generator recursing into the void, and a frozen browser tab is a worse sin than an imperfect board. The engineering answer was a wall-clock budget with a bounded fallback: if the search runs long, the generator returns a valid puzzle at the same grid size instead of chasing perfection forever. My public line on this hasn't changed and won't: never freeze the player to guarantee mathematical purity. You came here to think, not to watch a spinner spin.
The mistake that defines this game is one-dimensional thinking. Every digit in the grid sits at an intersection — it belongs to exactly one row and one column, and deleting it changes both totals at once. Players fix a row in isolation, feel the little win, then move to the next row, and the next, and around move six they look down and discover their columns are wrecked. Then they fix a column and break two rows. That seesaw is the game punishing greedy, line-by-line play. Every deletion is a double-edged move, and treating it as single-edged is how boards die slow deaths.
The way through is to plan at the intersections. Before deleting anything, compute each line's excess — how much its current sum overshoots its target. A row that needs to lose 9 and a column that needs to lose 9 might share a single 9 right at their crossing: one deletion, two problems solved. That's the ideal move in this game, and hunting for it is the real skill. Conversely, a digit sitting in a row that's already exact is untouchable, no matter how much its column wants it gone — which sometimes tells you an entirely different set of digits has to carry that column's loss instead.
Start small, and resist the first delete until you've read the excesses across the whole board. The grids get bigger, the intersections get denser, and the daily at midnight is the same board for every player on Earth. It's subtraction as strategy. Michael Scott would be proud of us all.