What it charges
Fees Rothera has collected, who pays them, and what that works out to per dollar of contract.
Fees per day
Who pays it
Rothera bills both sides of a matched trade, at different rates. This splits the exchange's daily take into the retail leg and the market-maker leg opposite it.
Cumulative
Effective rate
How this is measured
Fees here are computed, not reported. Rothera publishes no fee field. Every figure on this page is the venue's own published schedule applied to each individual fill on its trade tape — max(k × contracts × p × (1−p), $0.01) per side, rounded to the cent. Because it is billed per fill at the price that fill printed at, it is exact rather than an estimate.
Which is why the series starts where it does. Days before the tape have no trade prices, and every daily price proxy tested against them came out biased by −80% to +30%. Those days are left blank rather than filled in.
The two columns mean different things. “Fees per day”, “Cumulative” and “Effective rate” all plot what one retail trader pays to execute, which is the number comparable to Kalshi's. “Who pays it” plots what the exchange keeps, which is larger because Rothera bills both sides.
Why a fee rate moves at all. The schedule is a parabola in price, peaking at 50¢ and falling to nearly nothing in the tails, so an effective rate tracks where on the probability axis the venue traded rather than any change in what it charges.
Who is on each side is assumed, not observed. The tape carries no aggressor flag and no participant type, so the split above is the schedule's own model — one retail leg against one market-maker leg — applied to every fill. Rothera posts a third coefficient for professionals at six times retail, and a professional-heavy mix would put the exchange's take well above what is drawn here. This is the largest single uncertainty on the page.