Bid, ask, slippage and fees
Every option has a bid (the best price someone will pay) and an ask (the best price someone will sell at); trading at once means buying at the ask and selling at the bid, and that gap from the mid-price, plus the venue's trading fee, is the real cost of entering a trade.
Two prices, not one
An order book shows two prices for every option. The bid is the highest price a buyer is currently offering; the ask (or offer) is the lowest price a seller will accept. The mid-price is halfway between them, and the difference between the two is the spread.
The mid is a fair reference value, and it is what payoff charts and textbook examples use. It is not a price you can trade at immediately. If you want a fill now, you cross the spread:
- A leg you buy fills at the ask.
- A leg you sell fills at the bid.
That fill price is the execution price, and it is always worse than the mid for you. The gap between what a structure costs at mid and what it costs at execution is its slippage. You can try to do better by resting a limit order between bid and ask, but then you may not get filled at all.
Size at the top of the book
The bid and the ask each come with a size: how many contracts are actually offered at that price. That is the market's liquidity at the top of the book. If the ask shows 5 contracts and you want 20, only the first 5 fill at that ask; the rest climb to the next, worse price levels. Spreads are tight and sizes deep near the money and in the nearest expiries; far out-of-the-money strikes and long-dated expiries are thinner, with wider spreads and smaller sizes.
Trading fees
Crypto option venues charge a trading fee per contract, not a flat commission. The formula BOSS uses for all three venues is the same: a percentage of the underlying's price, capped at a percentage of the option's own price, so a cheap option is never charged a fee that eats a large part of its premium:
- fee per contract = min(0.03% × underlying price, cap × option price)
- The cap is 12.5% on Deribit and 7% on OKX and Bybit, from each venue's published regular-tier schedule.
With BTC at $100,000 the first term is $30. An at-the-money option worth thousands pays the full $30. A far out-of-the-money $120,000 call trading at $150 pays the cap instead: $18.75 on Deribit (12.5% of $150) or $10.50 on OKX and Bybit (7%). Fee schedules differ by account tier and change over time, so BOSS shows them as estimates.
A worked example: a long straddle
BTC is at $100,000, and you buy a 14-day long straddle at the $100,000 strike on Deribit: one call and one put, each quoted at $3,850 bid and $3,950 ask (a $3,900 mid, about 50% implied volatility).
| Item | Call | Put | Total |
|---|---|---|---|
| Mid-price cost | $3,900 | $3,900 | $7,800 |
| Execution cost (at the ask) | $3,950 | $3,950 | $7,900 |
| Slippage | $50 | $50 | $100 |
| Estimated fees | $30 | $30 | $60 |
| Total estimated cost | $3,980 | $3,980 | $7,960 |
At mid the straddle's breakevens would be $100,000 ± $7,800, that is $92,200 and $107,800. Paid at execution with fees they move out to $92,040 and $107,960: BTC has to travel $160 further before the trade makes anything. On one trade that is small; on a strategy that is traded often, or one with four legs instead of two, it adds up fast. And closing the position later crosses the spread again, the other way.
How BOSS uses this
Every strategy page's Estimated Cost to Assemble card shows exactly this breakdown, leg by leg: mid-price cost, execution cost, slippage, estimated fees and the total. The legs table shows the size available on the side each leg trades. The Scanner, Paper trading and the backtest all price at execution, ask to buy and bid to sell with fees included, because ranking on mid prices was misleading: some structures that looked profitable at mid couldn't make money at all once the spread and fees were paid. Comparing the same contracts across venues, as in cross-venue pricing, is also done at execution.
Spreads matter most for structures with many legs and a small edge, like a short iron condor: four spreads crossed to collect one modest credit.
Live on BOSS
A live long straddle at the money on the selected venue. Look at the Estimated Cost to Assemble card: the gap between the mid-price cost and the total is what crossing the spread and paying fees adds, and the legs table shows how much size backs each price.
| Position? | Right? | Ratio | Strike | Expiry | IV? | Premium? | Fill Price? | Liquidity? | Est. Fee? |
|---|---|---|---|---|---|---|---|---|---|
| Long | Call | 1 | $86000.0000 | 09 Oct 2026 | 32.9% | $1591.4172 | $1634.4285 | 44.8000 | $25.8068 |
| Long | Put | 1 | $86000.0000 | 09 Oct 2026 | 32.9% | $1548.3749 | $1591.3854 | 33.9000 | $25.8062 |
Net cost, breakevens, the payoff chart and the scenario table are after costs: every leg filled by crossing the spread, estimated fees included -- the same numbers the Scanner ranks by.
Estimated Cost to Assemble
An estimate of what entering this structure right now would really cost: filling every leg by crossing the spread (the ask when buying, the bid when selling) instead of at the mid-price, plus an estimated exchange fee. Real fees and fills can differ from this estimate.
Compare venues
These exact contracts -- same strikes, expiries and ratios -- on every venue BOSS tracks for this currency, at execution: what selling (bid) or buying (ask) each leg there comes to, after that venue's own fee. Green marks the best venue for each leg and for the whole structure.
| Deribit this page | Bybit | OKX | |
|---|---|---|---|
| Long Call $86000.0000 · 09 Oct 2026 | $1660.2352$1634.4285 + fee $25.8068 · IV 32.9% · 44.8000 | $1620.8344$1595.0000 + fee $25.8343 · IV 32.9% · 4.2100 | $1617.0198$1591.2163 + fee $25.8035 · IV 32.4% · 54.7500 |
| Long Put $86000.0000 · 09 Oct 2026 | $1617.1916$1591.3854 + fee $25.8062 · IV 32.9% · 33.9000 | $1575.8344$1550.0000 + fee $25.8343 · IV 32.9% · 10.1200 | $1617.0198$1591.2163 + fee $25.8035 · IV 32.4% · 87.3100 |
| Index? | $85940.7600 | $85979.2101 | $85951.8000 |
| Mid-Price Cost | $3139.7921 | $3132.5000 | $3139.4267 |
| Slippage? | +$86.0217 | +$12.5000 | +$43.0058 |
| Estimated Fees? | +$51.6130 | +$51.6687 | +$51.6070 |
| Total Estimated Cost | $3277.4268 | $3196.6687$80.7600 better than this page | $3234.0396$43.3900 better than this page |
| Max Profit? | Uncapped | Uncapped | Uncapped |
| Max Loss? | -$3277.4268 | -$3196.6687 | -$3234.0396 |
| Breakeven(s)? | $82722.5732, $89277.4268 | $82803.3313, $89196.6687 | $82765.9604, $89234.0396 |
| Structure IV? | 32.9% | 32.9% | 32.4% |
| Open on this venue → | Open on this venue → |
Each leg: what it nets there per contract (fill price with the fee folded in), then the fill price, fee, IV and the size quoted at that price.
Cross-venue differences
- Long Call $86000.0000 · 09 Oct 2026: OKX $1617.0198
- Long Put $86000.0000 · 09 Oct 2026: Bybit $1575.8344
| Contract | Best sale | Best purchase elsewhere | Difference | Size | IV spread (points) |
|---|---|---|---|---|---|
| Call $86000.0000 · 09 Oct 2026 | $1554.1656 Bybit | $1617.0198 OKX | -$62.8542 | 11.2200 | 0.5 Bybit 32.9% / OKX 32.4% |
| Put $86000.0000 · 09 Oct 2026 | $1522.4069 OKX | $1575.8344 Bybit | -$53.4274 | 10.1200 | 0.5 Bybit 32.9% / OKX 32.4% |
For comparing prices, not a recommendation: quotes move by the second, size is only what's shown at the top of the book, fees are each venue's published estimate, and the venues settle against different indexes and margin separately.
Market Context
This expiry as the Dashboard sees it: how the legs are priced against at-the-money and realized volatility, and where the expiry's forward sits against spot.
Volatility Smile?
Implied volatility across strikes at this expiry; the marked lines are this structure's strikes. Buying on the high part of the curve pays up for volatility; selling there collects it.
Leg bought Leg sold
Payoff & Greeks vs. Underlying Price
The Greeks curves are a Black-Scholes model using each leg's current implied volatility, holding time to expiry fixed -- not live exchange data at every price, which only exists at the current price (dashed line).
Payoff at Expiration
After costs At mid price
This structure's value and profit/loss at expiration, at a handful of specific prices: every leg's strike, every breakeven, the current spot, and the chart's own range.
| Underlying Price | Value at Expiration | Profit / Loss | Return on Cost |
|---|---|---|---|
| $68800.0000 | $17200.0000 | $13922.5732 | +424.8% |
| $82722.5732 breakeven | $3277.4268 | $0.0000 | +0.0% |
| $86000.0000 current | $0.0000 | -$3277.4268 | -100.0% |
| $89277.4268 breakeven | $3277.4268 | $0.0000 | +0.0% |
| $103200.0000 | $17200.0000 | $13922.5732 | +424.8% |
Delta (model)?
Gamma (model)?
Vega (model)?
Theta (model)?
Rho (model)?
Common mistakes
- Planning a trade at mid-prices. Immediate fills happen at the ask when buying and at the bid when selling.
- Counting the spread only once. Opening and closing a position before expiry both cross it.
- Ignoring size at the top of the book: a large order fills only partly at the quoted price and the rest at worse levels.
- Assuming the fee is a fixed commission. It is a percentage of the underlying, capped at a percentage of the option price, and differs by venue.
- Trading many-legged structures in thin, far-dated strikes, where wide spreads can consume most of the expected edge.
Where this shows up on BOSS
Educational content, not investment advice. See the disclaimer.