Kalshi Fee Calculator, including the rounding

The three formulas, as published

Work out a fee

All three coefficients compute side by side, with the unrounded and charged figures separate, so you can see what the ceiling added.

One fill only. Trading out before expiry adds a second fee at the exit price, rounded up separately: a round trip at 50 cents on 10 contracts costs 18 plus 18 cents, so 7.20 per cent of a 5 dollar stake.

Why it is a curve and not a percentage

The formula is quoted per contract, but you size a position in money, not in contracts. Since C = stake / P, substitute that in and the price term cancels:

Two things follow. The fee per contract is a parabola peaking at 50 cents: 0.07 × 0.5 × 0.5 = 0.0175, so 1.75 cents is the most a taker pays per contract, falling to 0.33 cents at both 5 and 95 cents. But the fee as a share of stake is not symmetric: 6.65 per cent at 5 cents against 0.35 per cent at 95 cents, a nineteen-fold span from one coefficient.

So a flat threshold cannot screen trades. An identical 2 per cent gross edge clears a 0.70 per cent break-even at 90 cents and cannot cover 5.60 per cent at 20 cents.

What the rounding costs, and where it bites

Rounding up to the next cent means any fill that generates a fee at all pays at least one cent: a raw 0.007 dollars becomes a charged cent. That is an effective minimum fee, and it is invisible in the formula. Take the extreme. One contract at 1 cent is a one cent stake, and the raw fee is 0.07 × 1 × 0.01 × 0.99 = 0.000693 dollars, rounded up to one cent. The fee equals the entire stake. The same single contract at 50 cents is a 50 cent stake with a raw fee of 1.75 cents, charged at 2 cents, so 4.00 per cent. Same coefficient, same rule, twenty-five times the cost.

Why longshots and not favourites: the round up adds at most one cent, so its cost as a share of stake is bounded by one cent over the stake. On a cheap contract a given contract count is a small stake, so that cent lands on a small denominator. At 99 cents the raw fee is just as small, the parabola being symmetric, but the stake is ninety-nine times larger.

The cost is not smooth either. Compare 4 cents and 5 cents in the table: it falls to 0.78 points, then rises again to 1.35, because it depends on how far the raw figure happens to sit below the next cent. That also produces real step changes in sizing. Four contracts at 3 cents has a raw fee of 0.8148 cents, charged as one cent against a 12 cent stake, so 8.33 per cent. A fifth contract makes it 1.0185 cents, charged as two cents against a 15 cent stake, so 13.33 per cent. The position grew by a quarter and the fee doubled.

Maker or taker is worth four times the fee

0.0175 against 0.07 is exactly a factor of four, so on Kalshi whether you rest an order or take the market matters more to your fee than anything else you control, including which market you trade. A taker at 50 cents needs 3.50 per cent of stake to break even; a maker needs 0.88. Two qualifications, both from the rounding.

• On small orders the gap collapses, and can vanish. At 1 cent a 10-contract taker order has a raw fee of 0.693 cents and a maker order 0.173 cents. Both round up to one cent: the same fee. The maker discount at that price does not appear until 15 contracts, where the taker figure crosses a cent and the maker figure has not, giving 2 cents against 1. At 14 contracts and below, making and taking cost identically.
• The factor of four is an asymptote approached from below. At 10 contracts and 50 cents it is 18 cents against 5, a ratio of 3.6. At 100 contracts, 1.75 dollars against 44 cents, 3.98. At 1,000 contracts, 17.50 dollars against 4.38, 3.995.

Being four times smaller, the maker fee is four times more likely to be swallowed by the ceiling, and resting orders are often small and often at longshot prices. The discount is real, and smallest where it would help most.

The half rate on INX and NASDAQ100

Trade Kalshi's S&P 500 or Nasdaq-100 markets at the standard 0.07 and you will overestimate your fees by close to a factor of two. The schedule carves those tickers out at 0.035, by prefix rather than by category: INXD, INXW, INXM, INXY, INXU, the matching NASDAQ100 series, and the KX-prefixed forms of both.

Worked, on 100 contracts at 50 cents. Standard rate: 0.07 × 100 × 0.25 = 1.75 dollars, charged as 1.75. On INXD: 0.035 × 100 × 0.25 = 0.875 dollars, charged as 88 cents, not 87.5. So the charged half-rate fee is 50.3 per cent of the charged standard fee, not exactly half. "Half rate" describes the coefficient, not the amount.

One honesty note. The carve-out wording we verified states the taker formula, so we apply the half rate on the taker side only and assert no half maker rate for index markets, because we have not verified one.

Break-even at every price

The curve as a table. Break-even is the gross move you need as a percentage of the money at risk, and it is rate × (1 - P) in every row. These are unrounded figures, so they are what a large order pays; for a small order, add the rounding cost from above.

How this differs from Polymarket

Both venues price fees with the same shape, rate × P × (1 - P) per contract, which makes the differences easy to state. There are three.

• Makers. Polymarket makers pay a verified zero, not a discount: across 600 markets read from the Gamma API on 31 July 2026, every published fee schedule carried takerOnly set to true. Kalshi makers pay 0.0175 on the same curve as takers.
• Rounding. Kalshi rounds up to the next cent. Polymarket documents no rounding, so its fee is charged as computed, which makes everything in the rounding section above Kalshi-only.
• Rate source. Kalshi has one taker coefficient plus the index carve-out. Polymarket's varies by category: 7 per cent crypto, 5 per cent sports, economics, culture, weather and other, 4 per cent finance, politics, technology and mentions, zero on geopolitical.

Numbers, on the same 10 contracts at 50 cents. Kalshi taker: 18 cents. Polymarket crypto taker: 17.5 cents, charged as computed, so on the one category where the coefficients match, the whole difference between the venues is half a cent of rounding. Polymarket politics: 10 cents. Geopolitical: nothing. Maker side: 5 cents against zero.

Polymarket fee calculator, with the per-category rates

Sources

We check against the CFTC filing rather than the help page, a filing being the more stable source. When a coefficient changes we will publish what it was, what it became, and the date we noticed. Of the eleven competitor pages we audited, none has ever published a correction.

Nothing on this page is financial advice, and prediction markets are not legal everywhere. Last updated 11 August 2026.