For options traders on Polymarket

The options market already prices Polymarket's S&P contracts. See where they disagree.

Paste a Polymarket link and two option quotes from your broker. OptionBridge reads the volatility smile, prices the contract, and tells you whether YES or NO is cheap after the spread you actually pay.

Open the calculator — free

Runs in your browser. No account needed.

Example SPY closes above $760 · 6.5 h left
Options fair value — —
Polymarket YES ask — —
— —
Inputs: SPY 758.40, 755 and 765 calls (IV 13.8% and 12.6%). Illustrative numbers, not a live market.

How it works

  1. Paste the market

    Drop in any Polymarket link for an S&P 500 or SPY contract. The strike, the type of contract, the resolution time and the live order book fill in for you.

  2. Add two option quotes

    From your broker's chain, take one strike just below the level and one just above, with expiry as close to resolution as you can get. Bid and ask are enough.

  3. Read the net edge

    You get the option-implied price of YES, and the edge on each side in cents per $1 contract, after the ask you would pay and any fee.

Priced the way a desk would price it

A binary on the S&P is a digital option. Getting it right takes more than plugging one volatility into Black-Scholes.

Skew included
The digital is the slope of the call price across strikes, so the smile matters: D = e−rTN(d2) − vega · ∂σ/∂K. Ignoring put skew understates upside contracts by several cents.
The price you can actually get
Edge is measured against the live ask on each side of Polymarket's order book, including fills against the opposite side, not against a mid you can't trade.
Exact clocks
Time to resolution is counted in hours and minutes. A same-day contract at 10:00 New York is very different from one at 15:30.
Every contract style
Closes above, closes below, closes in a range like $6,500–$7,000, and touch contracts, each with its own pricing.

Questions

Is this trading advice?

No. OptionBridge converts option prices you enter into the risk-neutral value of a binary contract. That is a pricing relationship, not a forecast. Hedging, liquidity, fees and the contract's exact resolution rules are yours to judge.

Which markets work?

Contracts on an index or ETF level that has listed options: S&P 500 (SPX), SPY, Nasdaq-100 and so on. Up/down and other contracts without a fixed level aren't supported.

Why does the resolution source matter?

Some Polymarket contracts settle on the official close, others on a price feed sampled at a set time. The calculator shows each market's source. Check it matches the options you are comparing against.

Where does my data go?

Nowhere. Calculations run in your browser. The only network requests are read-only price lookups to Polymarket's public API when you paste a link.

Why two option strikes?

One strike gives you the volatility level. Two give you the slope of the smile at the contract's level, which changes the binary's value. With one strike the calculator still works and warns you skew is missing.