How we check.

The same question on both apps.

Kalshi, Polymarket and Polymarket US often list the same question: who wins a game, who wins a vote, who wins an award.

The Oracle compares three apps: Kalshi, Polymarket and Polymarket US, a separate app with its own prices, fees and rules. A pick can use any two of the three apps, so you need an account on both apps it names. Each app sets its own rules on who can trade there.

We compare every open question on one app with every open question on the others and keep the ones that look alike. Then we read both apps’ rules side by side: what counts, who decides the result, and on which day. A pair only reaches the page when the rules say the same thing, or when they differ in one rare case that we can name for you.

By our estimate from a sample, about 1 in 5 Polymarket questions that end in the next two months has the same question on Kalshi. We are testing a computer program that reads both apps’ questions and suggests more matches. Our strict rule check always has the final say: in our test it caught 3 of 49 “same question” calls that were wrong on the rules.

Same words, different rules.

Two questions can read the same and still pay differently.

When the rules differ in one rare case, the card names it under Could go wrong, with what you would get back in that case at your amount and a rough chance, marked “our estimate” when it is our judgment. When we can’t name the case, we don’t show the pick.

Fees come first.

Both apps take a small fee when you buy. It is biggest on coin-flip questions, priced near 50¢, and small near 1¢ or 99¢.

On a coin-flip game the two fees add up to about 3¢ per $1. Fees can reduce or erase a quoted gap, so the Oracle subtracts them before it lists a pick:

Before fees this pair costs 97¢ and pays $1: it looks like 3¢ of free money. After both fees it costs about $1.00, and nothing is left. Every number on the Oracle is after both fees.

On 25 Sep, in one check of 1,124 games listed on both apps, 13 still showed a gap after fees. 9 of those games had already started, 1 was a mismatch and 1 was gone on a second look, so only 2 were real before the game began. The Oracle page shows the count from its own latest check.

How much is for sale.

Each app sells only so much at the best price. After that the price goes up and the gap shrinks.

We count how many pairs you can buy before the gap is gone. That is the “Only $… is for sale at this price” line on a card. Putting in more than that does not earn more: the Oracle works out your pick at the amount that fits and tells you so.

We also check the smallest order each app takes, so a pick never asks you for less than an app will sell.

How fresh the prices are.

In an observed sample, a typical short fast gap lasted about 11 minutes, and half of the sampled fast gaps were gone before the next half-hour check.

Discovery and live quote checks are separate. A completed scan establishes discovery time; supported quote checks can run every few seconds without discovering new markets. Where a live discovery watcher is enabled, a newly published gap is marked Just found. Between-scan discovery depends on that watcher being active. Use each card’s checked time and stale state, not the page-load time:

On picks that pay within a week, the buy buttons only work when the price is at most 15 seconds old and has passed two checks at least 5 seconds apart. Games already being played are never shown: every gap during a game that we re-checked was gone a moment later, 17 of 17.

Things that look like free money but aren’t.

These pairs look like a gap on paper. We skip them, or take them only when both apps’ rules match.

What we never do.

• We never hold your money. You buy on each app yourself, and each app pays you.
• We never place orders and never ask for your login, password or keys.
• We have no accounts. Your amount and My picks stay on your own device.
• We never suggest a way around any app’s rules.
• We never promise a result. A pick can still go wrong in the rare case its card names, and an order can fill at a worse price than we saw. This is not financial advice.