Kalshi fee calculator
Before you size anything, know what you have to be right about. This is the taker fee (Kalshi's published formula: round up 7% × contracts × price × (1 − price)), the total at risk, and the win rate you need just to break even.
Buying at 90¢ means the market already implies a 90% chance. You have to believe it is 90.63% or better just to break even — that gap is why sub-5¢ edges lose money slowly.
Why the breakeven matters more than the fee
At 50¢ the fee is largest: 7% × 0.5 × 0.5 = 1.75¢ per contract, asymptotically. Kalshi rounds the fee up to the next cent, once per order, so a single contract costs 2¢ — that rounding only fades as the order grows. At 90¢ the fee is 0.63¢, rounded to 1¢, so the honest breakeven is 91.0%, not the 90.6% the un-rounded number would give you. That asymmetry — small edges, real fees — is why the toolkit refuses to trade below a fee-aware floor. (We checked this against 149 real fills: the per-order form matches to the cent, while rounding per contract over-states the same fills by 39%.)
Measure the edge before you take it
The free playbook covers the setup traps. The full guide covers spend control, API drift, the dashboard, and the paper-first protocol.