When you buy a prediction market contract, your capital is locked until the market resolves or you sell your position. Whether that locked capital earns anything while it sits there depends entirely on which platform you are using and how the collateral is structured. The short answer is that most prediction market platforms do not automatically pay interest on open positions, and the ones that do have important conditions attached. The longer answer involves understanding what your capital is actually doing while a position is open and how to calculate what that idle time is costing you.
For the foundational explanation of how prediction market mechanics work before diving into capital efficiency, what are prediction markets covers the complete structure.
This matters more than most traders realize. A position held for six months in a slow-moving market is not just a directional bet on an outcome. It is also a decision to forego whatever that capital could have earned elsewhere. That foregone return is your opportunity cost, and it belongs in your expected value calculation before you enter any long-duration trade.
What Happens to Your Capital When You Buy a Prediction Market Contract
On most prediction market platforms, buying a YES or NO contract requires you to post the full cost of the contract upfront as collateral. On Polymarket's global platform, that collateral is USDC held on the Polygon blockchain. On Kalshi, that collateral is held in your Kalshi account balance.
In both cases, the capital is committed from the moment you enter the position until you either sell the contract or the market resolves. You cannot use the same capital for another trade while it is tied up in an open position. That is the basic structure that creates opportunity cost.
The question of whether you earn anything on that committed capital depends on the platform's collateral management model.
Does Polymarket Pay Interest on Open Positions?
Polymarket's global platform does not pay interest on collateral held in open positions.
Your USDC sits committed to your position on the Polygon blockchain. It earns nothing while the position is open. The only way to access the capital before resolution is to sell your position into the order book at the current market price.
The April 2026 migration to pUSD, Polymarket's platform-native stablecoin backed 1:1 by USDC, did not change the interest structure for open positions. pUSD held as position collateral does not earn yield. pUSD sitting uninvested in your account balance is similarly not earning interest under the current model.
This is a meaningful structural cost on long-duration markets. A trader holding a position in a year-end price target market from January through December is committing capital for up to twelve months with no yield on the collateral during that period.
Does Kalshi Pay Interest on Open Positions?
Kalshi's model is different, and the distinction matters for how you calculate opportunity cost.
Kalshi offers interest on uninvested cash balances in your account, currently at 3 to 4% APY depending on the current rate environment. That interest applies to cash sitting in your Kalshi account that has not yet been deployed into a position.
However, once capital is committed to an open contract, the position itself does not earn interest. The collateral backing your open contracts is not generating yield on your behalf while the position is live.
The practical implication: cash sitting idle in your Kalshi account earns something. Cash deployed into an open position does not. That distinction creates a specific calculation for any Kalshi trade where you are choosing between deploying capital now versus holding it in cash and waiting.
How to Calculate Opportunity Cost on a Prediction Market Position
Opportunity cost is what you give up by choosing one option over the next best alternative. For a prediction market position, the most relevant alternative is typically a low-risk yield-bearing instrument: a money market fund, a Treasury bill, or in the case of USDC, a stablecoin yield product.
The formula is straightforward.
Opportunity cost = capital deployed x annualized alternative yield x holding period in years
A concrete example: you deploy $1,000 into a Polymarket position that you expect to hold for six months. The current yield on a comparable low-risk alternative, say a short-duration Treasury or a USDC yield product, is 4.5% annualized.
Opportunity cost = $1,000 x 0.045 x 0.5 = $22.50
That $22.50 is the yield you are forgoing by committing that capital to the prediction market position for six months. It is not a fee you pay. It is a return you do not receive. But it belongs in your trade analysis the same way a transaction cost does.
Why This Matters More for Long-Duration Markets Than Short Ones
The opportunity cost calculation scales with holding period. A position that resolves in 24 hours has a negligible opportunity cost even at a high alternative yield. A position held for twelve months on a year-end outcome has a meaningful opportunity cost that can represent several percentage points of the capital deployed.
At a 4.5% alternative yield, a twelve-month position on $1,000 carries $45 in opportunity cost. On a contract priced at $0.70 where your maximum profit is $300, that $45 represents 15% of your potential gain simply from the cost of having capital idle rather than earning yield elsewhere.
This does not mean long-duration positions are not worth taking. It means your edge needs to be large enough to justify both the risk of the position and the opportunity cost of the capital.
How to Incorporate Opportunity Cost Into Expected Value
Standard expected value calculation for a prediction market position:
EV = (probability of YES x profit per share) minus (probability of NO x cost per share)
A more complete calculation incorporates opportunity cost:
Adjusted EV = standard EV minus opportunity cost over holding period
Example: you buy YES at $0.35 on a market you believe has a 50% true probability of resolving YES. You expect to hold for six months. You are deploying $350 to buy 1,000 shares.
Standard EV per share: (0.50 x $0.65) minus (0.50 x $0.35) = $0.325 minus $0.175 = $0.15 per share
Total standard EV on 1,000 shares: $150
Opportunity cost over six months at 4.5% annualized: $350 x 0.045 x 0.5 = $7.88
Adjusted EV: $150 minus $7.88 = $142.12
In this example the opportunity cost is small relative to the expected gain because the edge is large. But on markets where the edge is thin, say 2 to 3 percentage points of implied probability, the opportunity cost of a six to twelve month hold can consume most or all of the theoretical edge.
For a systematic methodology on identifying where market prices diverge from reasonable probabilities in long-duration markets, how to find mispriced markets on Polymarket covers the complete framework.
The Near-Certainty Problem: When High-Probability Markets Have Negative Adjusted EV
This is the scenario where opportunity cost most visibly changes the trading decision.
Suppose a market is trading at $0.95 on an outcome you believe has a 97% true probability of occurring. The market resolves in eight months.
Standard EV per share: (0.97 x $0.05) minus (0.03 x $0.95) = $0.0485 minus $0.0285 = $0.02 per share
On $950 deployed to buy 1,000 shares, total standard EV: $20
Opportunity cost over eight months at 4.5% annualized: $950 x 0.045 x 0.667 = $28.51
Adjusted EV: $20 minus $28.51 = negative $8.51
The position has positive standard expected value but negative adjusted expected value once you account for what the capital could earn elsewhere during the eight-month hold. The market looks like a good trade until you price in the opportunity cost of committing $950 for most of a year to earn $20 in expected profit.
This calculation changes depending on your alternative yield rate. At 2% annualized, the same position has an opportunity cost of $12.67 and a positive adjusted EV of $7.33. At 6% annualized, the opportunity cost rises to $38 and the negative adjusted EV deepens.
The current yield environment matters for how you evaluate near-certainty positions on long-duration markets.
Platforms That Do Pay Yield on Collateral: What Exists and What to Watch
A small number of prediction market adjacent platforms have experimented with yield-bearing collateral structures where the collateral backing open positions earns interest during the holding period. The mechanics typically involve the platform investing collateral in Treasury bills or money market instruments and passing some or all of the yield back to position holders.
This model is structurally more favorable for traders because it reduces or eliminates the opportunity cost of holding positions. However, it introduces additional counterparty risk: you are trusting the platform to invest collateral responsibly and to return both principal and yield correctly on resolution.
As of mid-2026, neither Polymarket nor Kalshi pays yield on the collateral backing open positions in their standard trading structures. Kalshi pays interest on uninvested cash balances but not on deployed capital. Polymarket pays nothing on either deployed or idle balances in the standard account structure.
If yield-bearing collateral structures become more common in the prediction market space, they will change the opportunity cost calculation significantly and make long-duration positions more competitive with yield-bearing alternatives on a risk-adjusted basis.
The Exit Option: How Selling Changes the Opportunity Cost Calculation
One feature of liquid prediction markets that traditional fixed-term bets lack is the ability to sell your position before resolution. This exit option changes the opportunity cost calculation in an important way.
If you enter a position expecting an eight-month hold but the market moves in your favor within two months and you sell, your actual holding period is two months, not eight. The opportunity cost you actually incur is the two-month version, not the eight-month version.
This means that on liquid markets where you can realistically exit when a favorable price movement occurs, your expected holding period may be significantly shorter than the market's resolution date. When calculating opportunity cost for positions on liquid markets, consider using an expected holding period based on when you anticipate exiting rather than the maximum possible holding period.
On illiquid markets where the exit option is theoretical rather than practical, use the full resolution date as your holding period. A position you cannot sell at a fair price is functionally the same as a fixed-term commitment from an opportunity cost perspective.
Comparing Kalshi and Polymarket on Total Capital Efficiency
Taking all the above together, a side-by-side comparison of how the two major platforms affect your capital while positions are open.
The Kalshi idle cash interest matters most for traders who maintain a cash reserve on the platform between positions. It does not reduce the opportunity cost of capital that is actively deployed in an open trade.
For a direct comparison of how Kalshi and Polymarket handle capital efficiency across all market types, Kalshi vs Polymarket: Which Prediction Market Is Right for You? covers the full breakdown.
Frequently Asked Questions
Do prediction markets pay interest on open positions?
Most major prediction market platforms including Polymarket and Kalshi do not pay interest on the collateral backing open positions. Kalshi pays 3 to 4% APY on uninvested cash balances, but that interest stops applying to any capital once it is deployed into a contract. Polymarket pays no interest on either open positions or idle balances in its standard account structure.
How do I calculate the opportunity cost of a prediction market position?
Multiply the capital deployed by your annualized alternative yield rate by the expected holding period in years. For a $500 position held six months with a 4.5% alternative yield, the opportunity cost is $500 multiplied by 0.045 multiplied by 0.5, which equals $11.25. That amount represents the yield you forgo by committing capital to the prediction market position rather than a yield-bearing alternative.
When does opportunity cost make a prediction market position not worth taking?
Opportunity cost most visibly undermines a trade when the expected gain is small and the holding period is long. Near-certainty positions priced above $0.90 on markets that resolve six months or more in the future are the most common example. The expected profit per share is small by construction because the outcome is nearly certain. When you subtract the opportunity cost of committing capital for the full holding period, the adjusted expected value can turn negative even when the standard expected value is positive.
Does the exit option reduce opportunity cost on prediction markets?
Yes, on liquid markets. If you enter a position expecting an eight-month hold but sell after two months when the price moves in your favor, you only incur two months of opportunity cost rather than eight. On illiquid markets where you cannot practically exit at a fair price, the full resolution date governs your opportunity cost calculation regardless of when you intended to exit.
The Bottom Line
Prediction markets do not pay interest on open positions. Your capital earns nothing while it is committed to a contract, which means every open position carries an opportunity cost equal to what that capital could have earned in a yield-bearing alternative during the same period.
For short-duration markets that resolve in days or weeks, the opportunity cost is negligible. For long-duration markets that resolve in months or years, the opportunity cost is a meaningful input to the trade analysis and can make theoretically positive-EV positions unattractive on a risk-adjusted basis.
The calculation is straightforward: capital deployed multiplied by alternative yield rate multiplied by holding period. Run it before entering any position you expect to hold for more than a month. On near-certainty positions with small potential gains and long holding periods, the opportunity cost may be larger than the expected profit.
For a complete overview of Polymarket trading strategies across all market types including macro, sports, and crypto, Polymarket trading strategies covers the full framework. For the best crypto prediction market platforms and how they compare for capital efficiency, best crypto prediction markets cover the complete landscape.
