Trading event contracts is speculation. You can lose everything you deposit, and most retail accounts do lose over time. Every strategy below can lose money. Only trade with cash you can afford to lose entirely, size positions tiny, and never chase losses.
The one idea everything rests on: price = probability
On a binary market, the price of a "Yes" contract is the market's implied probability. A contract at 90¢ means the market thinks there's about a 90% chance. It pays $1.00 if it happens, $0 if not. You only have a real trade when your honest probability differs enough from the price to overcome fees. Everything below is a way to find and exploit that gap — or to lock in a guaranteed one.
Strategy 1 — The "favorite grind" (buying at ~90¢)
This is the approach a lot of new traders gravitate to: buy heavy favorites at a high price — say 90¢ — and collect the small, frequent payout when they win. Here's the honest math you must understand before you try it.
- Buy a contract at 90¢. If it wins, you get $1.00 — a 10¢ profit on 90¢ risked ≈ 11% return.
- If it loses, you lose the full 90¢.
- So one loss wipes out roughly nine wins. That's the trap hiding inside "safe" favorites.
The strategy is only profitable if the favorite's true win probability is higher than 90% plus your fee. At Kalshi's ~7% on winnings, a 10¢ gross win nets closer to 9.3¢, so you need the favorite to win noticeably more than 90% of the time just to break even. Buying 90¢ contracts on a hunch is not "safe income" — it's a bet that the market has underpriced a near-certainty.
How to use averaging honestly
The disciplined version: build a basket of many favorites you've each judged to be truly higher-probability than their price, then track the average outcome. If you buy 20 contracts averaging 90¢ and 19 win, your average payout is $0.95 against a 90¢ cost — a real edge. If only 17 win, you've lost money. The average across many trades — not any single win — tells you whether you actually have skill or are just collecting small wins until one blowup erases them. There's a well-documented "favorite-longshot bias" where favorites are often slightly underpriced and longshots overpriced, but it's thin and fees can eat it — verify it in your own logged results before scaling.
The favorite grind feels like easy money because you win most days. That's exactly why it's dangerous: a string of green days lulls you into oversizing, then a single upset at 90¢ erases weeks of gains. If you run this, size each position tiny and treat the rare loss as the whole point of the math — not a fluke.
Strategy 2 — Cross-platform arbitrage
The closest thing to "guaranteed" — and still not risk-free. The same real-world event is often priced differently on Kalshi vs Polymarket, with 2–5% gaps on major events. If you can buy "Yes" on one venue and "No" on the other for a combined cost under $1.00, you lock a payout regardless of the outcome.
- The math: basket cost = (Yes price on A) + (No price on B). Your edge = $1.00 − cost − fees. If Yes is 48¢ on Kalshi and No is 49¢ on Polymarket, the basket costs 97¢ — a 3¢ gross edge before fees.
- Position size: limited by order-book depth or your bankroll — take the smaller of (available contracts) and (bankroll ÷ cost).
- The catches: fees can erase a thin gap; the two legs must settle on identical terms (wording differences can break the "guarantee"); crypto transfers add time and gas; and capital is tied up on two platforms at once. A 3¢ gap after a 7% fee on the winning leg may not survive.
Arbitrage is real but competitive — bots hunt the obvious gaps in seconds. Retail arbers win on markets too small or too new for bots, and only when they've priced fees precisely.
Strategy 3 — Value (directional) trades
Buy "Yes" on something you believe is underpriced, or "No" on something overhyped. The bar: most disciplined traders require an edge above ~8% — your probability must beat the price by at least that — before placing a trade, because smaller gaps get eaten by fees and error in your own estimate. Edge comes from doing work the crowd hasn't (reading primary sources, tracking under-covered markets), not from vibes or headlines already in the price.
The math that keeps you solvent: Kelly sizing
Position sizing decides whether an edge ever compounds or a losing streak wipes you out. The Kelly criterion tells you the theoretically optimal fraction of bankroll to bet given your edge — but full Kelly is brutally volatile, so professionals use a fraction of it:
- A 58% probability at a 54¢ price sizes to about 8.5% of bankroll under full Kelly.
- Half-Kelly cuts that to ~4.25% and roughly halves your drawdown swings — the realistic default.
- Many cap positions at 5% of bankroll using fractional Kelly (often 0.25×) specifically to survive losing streaks.
Translation for a $500 bankroll: even a strong edge rarely justifies more than ~$20–$25 in a single position, and $5–$15 is more typical. The point of small sizing isn't timidity — it's staying in the game long enough for your edge to show up. Run your true disposable number through our budget builder first and only trade with what's left after savings and bills.
Write down your probability estimate, the price, your reasoning, and the result for every trade. After 50+ trades, your log reveals whether your estimates are actually calibrated (do your "70%" trades win ~70% of the time?). Without a log you'll remember the wins, forget the losses, and never know if you have real skill. The log — not your P&L on a lucky week — is the truth.
Taxes
Net gains are taxable. Kalshi issues 1099-style forms; Polymarket's USDC settlement means tracking capital gains yourself. Log everything and set aside part of any winnings — estimate with the side hustle tax calculator and stay penalty-free with the quarterly tax estimator.
Bottom line
There's no free money here — the favorite grind hides blowup risk, arbitrage gaps are thin and contested, and value trades need real work to clear the fee hurdle. What separates a modest side income from a fast loss is discipline: convert everything to probability, demand a real edge, size with fractional Kelly, log every trade, and price in fees before you click. Pick your venue with our Kalshi vs Polymarket vs DraftKings comparison, see the theory in action in the World Cup and NBA Finals breakdowns, and find lower-variance income in the gig finder.