How much does an option's bid-ask spread cost me each time I enter and exit the trade?

How this is calculated

• Spread per share equals the ask price minus the bid price. Mid price equals the average of the bid and ask.
• The dollar cost per contract equals the spread multiplied by the contract multiplier (100 shares for a standard equity option). Total round-trip cost multiplies that by your contract count.
• This represents the cost of buying at the ask and immediately selling at the bid, the standard way to measure spread cost. Your actual fill may land between the bid and ask, so this is a worst-case-style estimate, not a guaranteed cost.
• Spread as a percent of the mid price is a useful comparison across different option prices. A wide spread on a low-priced option can be a much bigger drag than the same dollar spread on a high-priced one.
• As a general guideline, many liquid, actively traded options run a spread under 5% of the mid price, while thin or far-dated contracts can run 15% or higher. Treat this as a rough guide, not a fixed rule, since normal spreads vary by underlying and market conditions.