Prediction Market Profit Calculator
Calculate your real profit on Kalshi and Polymarket after all fees. Compare cross-venue trades and find the most profitable execution path.
TL;DR
Kalshi charges 1-7% on the lesser side of each contract (e.g. 7% of 40 cents on a 60-cent contract). Polymarket has zero taker fees but you pay Polygon gas ($0.01-$1.00 per tx). When cross-venue arbitrage exists, buying YES on one platform and NO on the other locks in guaranteed profit regardless of outcome. This calculator shows your real P&L after every fee. It pairs up with every guide in our prediction market cluster, so you can jump from math to strategy without leaving the site.
How Kalshi Fees Work
Kalshi uses a tiered fee structure that catches many new traders off guard. The fee isn't applied to the full contract price. Instead, it's calculated on the lesser of the buy price or its complement. In practice, this means:
Fee = fee_tier% × min(price, 100 - price)
If you buy a YES contract at 60 cents, the fee base is min(60, 40) = 40 cents. At the default 7% tier, that's 0.07 × 40 = 2.8 cents per contract. This design means fees are highest on contracts near 50 cents and lowest on contracts near 1 or 99 cents.
The same fee applies when you sell. If you buy at 55 cents and sell at 70 cents, you pay the fee twice: once on entry and once on exit. This double-fee hit is why short-term Kalshi trading requires wider edges than you might expect.
Kalshi Fee Tier Table
| Tier | Fee Rate | Monthly Volume Threshold |
|---|---|---|
| 1 (default) | 7% | $0+ |
| 2 | 6% | $50,000+ |
| 3 | 5% | $100,000+ |
| 4 | 4% | $250,000+ |
| 5 | 3% | $500,000+ |
| 6 | 2% | $1,000,000+ |
| 7 | 1% | $5,000,000+ |
The difference between tiers is massive. On a 50-cent contract, the 7% tier costs 3.5 cents per contract while the 1% tier costs just 0.5 cents. Over 1,000 contracts, that's $30 in saved fees, often the difference between a profitable and unprofitable trade.
How Polymarket Fees Work
Polymarket took a different approach: zero taker fees. You don't pay a percentage on trades. Instead, your costs come from two sources:
- Gas fees: Polymarket runs on Polygon L2, so each transaction costs a small gas fee (typically $0.01 to $1.00 depending on network congestion). You pay gas on every buy, sell, and redemption.
- Spread: You buy at the ask price and sell at the bid price. On liquid markets, spreads are 1-2 cents. On illiquid markets, spreads can be 5-10+ cents. This is an implicit cost that doesn't show up as a "fee" but directly impacts your profit.
Because Polymarket uses USDC on Polygon, you also need to factor in the cost of bridging funds if your USDC is on Ethereum mainnet. Bridging costs vary but can run $5-$20 during high gas periods. Once your USDC is on Polygon, transaction costs stay low.
Kalshi vs. Polymarket: Fee Comparison
Which platform is cheaper? It depends entirely on your trade size and price level.
For small trades ($10-$50), Polymarket's fixed gas cost is proportionally expensive. A $0.50 gas fee on a $20 trade is 2.5% of your position. Kalshi's percentage-based fee scales better for small trades near the extremes (prices near 5 or 95 cents).
For large trades ($500+), Polymarket dominates. That same $0.50 gas fee on a $1,000 trade is 0.05%. Kalshi's 7% tier on 100 contracts at 50 cents costs $3.50, seven times more expensive.
The breakeven point varies by Kalshi price and fee tier, but as a rule of thumb: Polymarket is cheaper for trades above ~$200 at the default fee tier. Use the calculator above to compare your specific scenario, or check our EV calculator to evaluate whether the edge justifies the fees.
Cross-Venue Arbitrage: The Real Opportunity
The most powerful use of this calculator is the Cross-Venue Arbitrage mode. When the same event trades on both Kalshi and Polymarket, pricing inefficiencies create risk-free profit opportunities.
Here's how it works: if Kalshi prices YES at 52 cents and Polymarket prices NO at $0.45, your total cost to cover both sides is $0.52 + $0.45 = $0.97. Since one side always pays out $1.00, you lock in $0.03 guaranteed profit per contract, no matter what happens.
The catch is fees. After Kalshi's fee on the 52-cent buy and Polymarket's gas, that $0.03 edge might shrink to $0.01 or even go negative. This is exactly why you need a calculator that accounts for both platforms' fee structures simultaneously. For a deeper dive on the mechanics, see our guide on Kalshi vs. Polymarket arbitrage.
Why Fees Matter More Than You Think
Most prediction market edges are small, typically 1-5%. At those margins, fees don't just reduce profit; they determine whether profit exists at all.
Consider a 3% edge opportunity: 100 contracts on Kalshi at 50 cents with a 7% fee tier costs you $3.50 in fees alone. That's 7% of your $50 investment eaten by fees, wiping out the 3% edge entirely. The same trade at the 3% fee tier costs only $1.50, preserving a net profit of $1.50.
This is why professional arbitrageurs obsess over fee optimization. Reducing your Kalshi tier from 7% to 3% can double or triple the number of profitable opportunities available to you. Learn more about finding these opportunities in our arbitrage calculator guide.
Real-World Examples
Example 1: Kalshi YES Win
You buy 200 YES contracts at 40 cents with a 7% fee tier. Fee base: min(40, 60) = 40. Fee: 0.07 × 40 = 2.8 cents/contract. Total fee: 200 × $0.028 = $5.60. Entry cost: 200 × $0.40 + $5.60 = $85.60. If YES wins, payout is 200 × $1.00 = $200. Net profit: $200 - $85.60 = $114.40. ROI: 133.6%.
Example 2: Polymarket Large Position
You invest $500 at a 0.60 price with $0.50 gas. Shares: $500 / $0.60 = 833.3. If YES wins, payout: 833.3 × $1.00 = $833.33. Net profit: $833.33 - $500 - $0.50 = $332.83. ROI: 66.4%. The gas fee is negligible at this size.
Example 3: Cross-Venue Arb
Kalshi YES at 48 cents, Polymarket NO at $0.49, 100 contracts, 7% fee tier, $0.50 gas. Kalshi fee: 0.07 × min(48, 52) = 3.36 cents. Kalshi cost: $48 + $3.36 = $51.36. Poly cost: 100 × $0.49 + $0.50 = $49.50. Total invested: $100.86. Payout (either outcome): $100. Net: -$0.86. No arb. Fees killed the edge. This is exactly why you need to calculate before you trade.
For more strategies on maximizing your edge, explore our odds converter to translate between formats, or read about building a prediction market trading bot that handles fee optimization automatically.
FAQ
How do Kalshi fees work?
Kalshi charges a percentage fee on each contract based on your fee tier (1% to 7%). The fee is calculated on the lesser of the buy price or (100 minus the buy price) in cents. For example, buying at 60 cents with a 7% fee tier: the fee base is min(60, 40) = 40 cents, so the fee is 0.07 × 40 = 2.8 cents per contract. New accounts start at the 7% tier and can reduce fees by increasing monthly trading volume.
How do Polymarket fees work?
Polymarket currently charges no taker fees on trades. The main costs are gas fees for transactions on the Polygon L2 network, which typically range from $0.01 to $1.00 per transaction depending on network congestion. You also pay the spread between the bid and ask price. Polymarket uses USDC as its base currency, and all settlements happen on-chain.
How do you calculate prediction market profit?
For Kalshi: profit = (payout − buy price per contract × number of contracts) − total fees. Each winning YES contract pays out $1.00. For Polymarket: profit = (shares × $1.00 if correct) − amount invested − gas fees. Shares are calculated as your dollar amount divided by the price per share. In both cases, subtract all fees and transaction costs to get your true net profit.
What is the spread on prediction markets?
The spread is the difference between the best bid and best ask price for a contract. On Kalshi, spreads typically range from 1 to 5 cents on liquid markets and can be 10+ cents on illiquid ones. On Polymarket, spreads vary by market liquidity but are generally tighter on popular events. The spread represents an immediate cost when entering and exiting positions, and it matters most for short-term trades or arbitrage where margins are thin.
Can you arbitrage Kalshi and Polymarket?
Yes. Cross-venue arbitrage between Kalshi and Polymarket is possible when the combined cost of buying YES on one platform and NO on the other totals less than $1.00 after all fees. For example, if Kalshi YES is 52 cents and Polymarket NO is $0.45, the total cost is $0.97, locking in a $0.03 guaranteed profit per contract regardless of the outcome. Claw Arbs detects and executes these opportunities automatically in under 20 milliseconds.
How do gas fees affect Polymarket profits?
Gas fees on Polygon L2 are relatively low (usually under $0.50 per transaction), but they become significant on small trades. For a $10 trade with $0.50 gas, you lose 5% to fees before the market even moves. For a $1,000 trade, that same $0.50 gas is only 0.05%. This is why larger position sizes are more efficient on Polymarket. When arbitraging across venues, always factor in gas for both the entry and exit transactions.