Build and Kill Zombies Roll Odds Calculator
Pick a part category and ladder slot โ from the 1-in-3 starter engine to the 1-in-12,500 endgame pull โ add your Luck skills, and see how many rolls each success target really takes. Every ladder here is read from the game's own Index and pickup popups.
Don't have a target yet? The Part & Build Finder picks your next documented part from what you already own โ then come back here to budget the grind.
What This Calculator Covers
The engine ladder is the only category fully read from the in-game Index so far โ ten slots from 1 in 3 to 1 in 12,500. Supports and weapons are included for the slots confirmed on camera (Wooden Spike 1 in 3, Flamethrower 1 in 9, Double Barrel 1 in 10). Slots nobody has read yet are never invented, so categories grow as footage confirms them โ the full tables with per-value evidence live on the builds & parts hub.
The maths treats each roll as independent at the displayed base rate, which is the same assumption the in-game Index odds display implies. What it does not model: Global Booster windows, event modifiers and any hidden pity system โ if the game runs one, it has not been documented.
Seen in footage ยท 2026-09-24How to Use the Numbers
- Plan rolls per session โ a 90% target on the 1-in-3 engine slot is about 7 rolls; the same confidence on a 1-in-40 slot is about 92. Budget cash accordingly before a rolling session.
- Buy Luck first โ Luck II costs 250 and Luck III costs 625 (see the skills guide); over hundreds of rolls they beat almost any single-part purchase.
- Codes fund the rolls โ the working codes on the codes page hand out free cash and even free parts, shrinking the effective number of rolls you need to pay for.
Roll Odds Calculator FAQ
How is the chance calculated in the roll odds calculator?
For a 1-in-N part the chance of missing a single roll is 1 โ 1/N, so after x rolls the chance of having seen it at least once is 1 โ (1 โ 1/N)^x. The calculator inverts that formula: enter the ladder slot and it returns the roll counts for 50%, 90% and 99% likelihood.
Does hitting the average number of rolls guarantee the part?
No. At the average (N rolls for a 1-in-N part) you are only around 63% likely to have seen it at least once. The calculator shows 50/90/99% targets so you can plan against a real goal instead of a coin flip.
How does Luck change the odds?
Luck shifts roll results toward the rarer end of each ladder. The calculator models the documented Luck II (+20%) and Luck III (+25%) skills as a proportional rate boost, which is an approximation โ the game has not published the exact luck formula, so treat luck-mode outputs as estimates (the base-rate table on the builds hub is the precise reference).
Where do the odds come from?
From the game itself: the in-game INDEX displays each category's odds ladder, and pickup popups show per-part odds and values. Every documented number on this site is read frame by frame from public gameplay footage and carries a source tag on the builds hub. Slots not yet read on camera are never guessed.
What to do with your results: assemble the parts into a car with the Build Mode walkthrough, plan the run with wave survival, and track new ladders on the update log.