Which prediction market app is biggest?

Polymarket, by volume and by breadth of coverage. That matters beyond bragging rights: deeper markets have tighter spreads and prices that better reflect available information.

Which ones are legal in the US?

Polymarket US and Kalshi both operate as CFTC-registered exchanges. PredictIt has long run under specific regulatory constraints. Manifold uses play money. State-level availability still varies for the real-money venues.

Not for the US venues — Polymarket US and Kalshi are USD-denominated with ordinary funding methods. The global Polymarket platform is crypto-denominated, and US users cannot access it.

Can I compare prices across platforms?

Yes, and you should when the same question is listed in more than one place. Market Guy tracks Polymarket and Kalshi side by side so the same question can be compared directly.

What are the best apps like Polymarket?

Kalshi is the closest comparison — a CFTC-regulated US exchange with real money and overlapping coverage, strongest on macro and economic data. PredictIt is the older US-politics venue, constrained by position caps. Manifold is the play-money option if you want the mechanics without the risk. Nothing else currently matches Polymarket on breadth.

What is a good PredictIt alternative?

For US politics with real depth, Polymarket. For anything tied to a scheduled data release, Kalshi. Both lift PredictIt's two binding constraints — the position caps and the thin liquidity that follows from them — while remaining accessible to US traders.

Which prediction market platforms exist besides the big two?

PredictIt and Manifold are the two worth knowing. Beyond them the field thins out quickly into venues with too little volume for their prices to mean much, which is the trait that matters more than the feature list.

Is there prediction market software or an aggregator that covers several venues?

Aggregation is a separate layer from the venues themselves: the platforms run the markets, an aggregator reads across them so the same question can be compared in one place. That is what Market Guy does for Polymarket and Kalshi — and reading the prices needs no account anywhere.

The best prediction market apps

Four platforms dominate the conversation and they are not competing for the same person. Here's what separates them.

9 min readUpdated Oct 15, 2026

Key takeaways

Polymarket has the most volume and the widest coverage. Polymarket US is a CFTC-registered, dollar-denominated exchange; the separate global platform is crypto-denominated and closed to US users.
Kalshi is the other CFTC-regulated US exchange, strongest on macro and economic data, and it issues some tax documentation.
PredictIt is held back by position caps and thin liquidity; Manifold uses play money — good for learning the mechanics, not a real probability estimate.
Reading the prices needs no account anywhere, and the venue with the most money on a question usually has the most trustworthy price.

The four platforms at a glance

Four venues dominate the conversation, and they are not competing for the same person. The table sorts out which is which; the sections below explain why each one is the way it is.

Regulatory status, fee schedules and state-level availability all change. This is a starting point — the operator's own current terms are the only authority.
Platform	Regulation	US access	Denomination	Strongest coverage	Tax paperwork
Polymarket	Polymarket US is a CFTC-registered exchange. The separate global platform operates outside that perimeter.	Yes, through Polymarket US, with full KYC. State-level availability still varies.	USD on Polymarket US; crypto on the global platform.	The broadest of the four — politics, sports, crypto, tech, culture and a long tail.	Not issued by the global platform. Check what Polymarket US provides.
Kalshi	CFTC-regulated US exchange, and the one that got there first.	Yes, with KYC.	USD.	Economics, weather, macro data releases, and increasingly sports.	Issues some tax documentation — the clearest paper trail of the four.
PredictIt	Long-standing regulatory constraints that cap position sizes and traders per market.	Yes, within those caps.	USD.	US politics, with years of price history to look back on.	Check the operator. Fees apply to both withdrawals and profits.
Manifold	None — it is a play-money platform, not a regulated venue.	Yes.	Play money.	Anything a user cares to create, which is the whole point.	Not applicable.

If you only take one thing from the table: the venue with the most money on a question usually has the most trustworthy price on it.

Polymarket

The largest by volume and the widest by coverage — politics, sports, crypto, tech, culture and a long tail of everything else. Polymarket US is a CFTC-registered exchange, USD-denominated with full KYC; the separate global platform is crypto-denominated and unavailable to US users.

Volume is the reason to care. Deep markets mean tight spreads and prices worth taking seriously, and Polymarket has the deepest on most big questions.

Best for: breadth, liquidity, and the biggest multi-outcome events.
Watch for: state availability, and the thin long tail where the spread bites.

Kalshi

The other CFTC-regulated US exchange, and the one that got there first. Kalshi leans into economics, weather, macro data and increasingly sports, with markets built around scheduled data releases — inflation prints, Fed decisions, jobs numbers.

It also issues some tax documentation, which Polymarket's global platform does not, and that alone makes it easier to live with for some people.

Best for: macro, economic data, and anyone who wants a paper trail.
Watch for: thinner volume than Polymarket outside its core categories.

PredictIt

The academic-lineage veteran, focused almost entirely on US politics and long operating under regulatory constraints that cap position sizes and the number of traders per market.

Those caps are the whole story: they keep it small, and small means prices can drift from where a deeper market would put them. Historically interesting, but it is no longer where the serious money prices elections.

Best for: US political markets with a long history to look back on.
Watch for: position caps, limited liquidity, and fees on both withdrawals and profits.

Manifold

Play-money by design. Anyone can create a market about anything, which produces enormous variety and a genuinely useful sandbox for learning how pricing works without risking anything.

Because there is no real money at stake, the calibration incentive is weaker — prices are directionally interesting and should not be treated as a real probability estimate.

Best for: learning the mechanics, and questions no regulated venue would list.
Watch for: play-money prices are not a substitute for a real market's estimate.

How to actually choose

If you want the most accurate live probability on a big question, go where the volume is — that is usually Polymarket. If you care about macro releases or want tax paperwork, Kalshi. If you want to learn without risk, Manifold. PredictIt is now mostly of historical interest.

One thing worth saying plainly: you do not need an account anywhere to use the prices. Reading the odds, comparing them across venues and doing research is free, and it is the part with the best return on effort.

Liquidity beats interface. The platform with the most money on a question usually has the most trustworthy price on it.

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How this was researched

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Frequently asked questions

Which prediction market app is biggest?: Polymarket, by volume and by breadth of coverage. That matters beyond bragging rights: deeper markets have tighter spreads and prices that better reflect available information.
Which ones are legal in the US?: Polymarket US and Kalshi both operate as CFTC-registered exchanges. PredictIt has long run under specific regulatory constraints. Manifold uses play money. State-level availability still varies for the real-money venues.
Do I need crypto?: Not for the US venues — Polymarket US and Kalshi are USD-denominated with ordinary funding methods. The global Polymarket platform is crypto-denominated, and US users cannot access it.
Can I compare prices across platforms?: Yes, and you should when the same question is listed in more than one place. Market Guy tracks Polymarket and Kalshi side by side so the same question can be compared directly.
What are the best apps like Polymarket?: Kalshi is the closest comparison — a CFTC-regulated US exchange with real money and overlapping coverage, strongest on macro and economic data. PredictIt is the older US-politics venue, constrained by position caps. Manifold is the play-money option if you want the mechanics without the risk. Nothing else currently matches Polymarket on breadth.
What is a good PredictIt alternative?: For US politics with real depth, Polymarket. For anything tied to a scheduled data release, Kalshi. Both lift PredictIt's two binding constraints — the position caps and the thin liquidity that follows from them — while remaining accessible to US traders.
Which prediction market platforms exist besides the big two?: PredictIt and Manifold are the two worth knowing. Beyond them the field thins out quickly into venues with too little volume for their prices to mean much, which is the trait that matters more than the feature list.
Is there prediction market software or an aggregator that covers several venues?: Aggregation is a separate layer from the venues themselves: the platforms run the markets, an aggregator reads across them so the same question can be compared in one place. That is what Market Guy does for Polymarket and Kalshi — and reading the prices needs no account anywhere.

Keep learning

Prediction markets carry real risk of loss. Nothing on Market Guy is financial advice — it is research tooling to help you think, not a signal to trade.