How the numbers are built.
Quotes come live from each venue's public API. “You save” is the difference
in all-in cost, not the difference in quoted price: Kalshi charges
0.07 × P × (1−P) per contract, which peaks near 50¢ and nearly
disappears at the extremes, so a better-looking quote is sometimes the worse
fill. Polymarket is modelled at zero trading fee, which matches these
markets today. Risk-free edge is only calculated where the listed outcomes
are mutually exclusive and cover every case — on a partial field,
buying every listed name does not guarantee a payout, so no number is shown.
A quote with no bid behind it is shown but never counted; the ask is an offer
nobody is matching. The budget box accounts for Kalshi rounding each order's
fee up to the next cent, which is why a thin edge can be real at size and
worthless on a handful of contracts. Both venues move — treat thin edges as
indicative, and check the book before you act.