About this tool
The Gacha Pity Calculator models a banner with a low base rate, a soft-pity ramp and a hard-pity guarantee, so you can see your real chance of landing a top-rarity pull. You supply the constants — base rate, soft-pity pull, hard-pity pull, and how many pulls you have — and everything is computed locally in your browser; no banner or account data is used.
The per-pull rate is the flat base up to soft pity, then ramps linearly each pull until it reaches 100% at hard pity. The chance of at least one success within N pulls is 1 − Π(1 − rᵢ) over those pulls, and the expected pulls to your first success is Σ i·P(first hit on pull i). Turning on the optional 50/50 featured toggle models the mechanic where half the time your first hit is the featured item and otherwise a second, guaranteed-featured hit is needed — computed by convolving the pity distribution with itself.
Enter your numbers to see the chance within N pulls, the expected pulls to hit, and how many pulls reach about a 90% chance. All constants are yours to set, so it works for any game's pity system rather than assuming a specific banner.