TL;DR
- Open interest tells you how many option contracts are still alive; volume tells you how many traded today. Use both to gauge liquidity before you enter.
- Look for open interest at least 10× the number of contracts you plan to sell. Anything thinner and you become the market.
- Tight bid-ask spreads, penny increments, and multiple strikes above 100 contracts are the green lights for a clean exit.
- Skip the first weekly after earnings and the monthly that expires in a holiday week. Liquidity drains faster than you think.
In the spring of 2007 I was feeling pretty good about myself. My account had doubled in fourteen months and I was selling covered calls the way most people check email – casually, every morning, without a second thought. Then came 2008. The market cracked, my stocks slid, and the premiums I thought were “free money” evaporated while the underlying kept falling. I learned, the hard way, that collecting 1.5 percent a month does nothing if the stock drops 40 percent and nobody wants to buy your calls back at any price. Liquidity vanished and I was trapped. That pain became the circuit-breaker rule, the liquidity checklist, and the very reason I still start every trade by staring at the open interest column before I ever click “sell to open.”
What Open Interest Actually Tells You
Open interest is the running tally of contracts that have not yet been closed or exercised. When I see 1,800 contracts open on a strike, I know there is a crowd. That crowd means I can get out when I want, at a price that is still close to the mid-point. Below 100 contracts, the crowd is a coffee klatch. I once tried to close ten contracts on a strike that had only twelve open. The bid was 0.05, the ask was 0.50, and I ended up paying 0.25 just to escape. That single trade cost more in slippage than I had collected in three months of premium. The lesson stuck: open interest is the oxygen of a position.
Volume Versus Open Interest – The Dynamic Duo
Volume is the one-day scorecard; open interest is the lifetime score. If open interest is rising along with volume, fresh money is entering and the strike is self-replenishing. If volume spikes but open interest shrinks, the smart money is closing-usually because something changed. I keep a simple side-by-side watch: last night’s open interest versus today’s volume. A ratio of 5-to-1 or higher tells me the strike is still liquid enough for a new round of covered calls. Anything under 3-to-1 and I walk.
Where to Find the Data and How to Read It
Every decent broker platform shows both numbers, but I still open a free site like cashflowmachine.io/covered-calls to double-check. The table I look at lists strike, last trade, bid, ask, volume, open interest, and implied volatility. I sort descending by open interest, then eyeball the bid-ask spread. A penny-wide spread on a two-dollar option is normal. A ten-cent spread on a two-dollar option is a billboard that says “thin ice.” If the spread is wide and the open interest is low, I treat that strike the way I treat a gas station sushi tray.
Three Liquidity Filters I Never Skip
Filter 1 – Absolute Size. I need at least 500 contracts open interest on any strike I touch. For weekly options, the number drops to 200, but only if I intend to hold through expiration. Anything less and the market maker can move the quote three cents just because I showed up.
Filter 2 – Relative Liquidity. The open interest must be at least ten times the size of my trade. If I am planning to sell 20 contracts, I want to see 200 open. That leaves room for me and the next guy without rocking the boat.
Filter 3 – Spread-to-Premium Ratio. I divide the bid-ask spread by the premium I expect to collect. If the ratio is above 5 percent, I pass. Life is too short to give up the first week of income to the spread. I walk through this calculation live every Wednesday on the Cash Flow Machine YouTube channel if you ever want to watch the numbers in real time.
Red Flags That Scream “No Trade”
Holiday weeks, earnings weeks, and triple-witching Fridays can all drain liquidity overnight. I also avoid strikes that are more than 20 percent out-of-the-money on low-volatility names; open interest tends to cluster near the current price, and the wings are ghost towns. Finally, any option chain where every strike shows exactly 1 contract of open interest is usually a market-maker test print. Step aside and wait for a real crowd.
How much open interest is enough for a covered call?
Shoot for at least 200 contracts on weeklies or 500 on monthlies, and make sure that number is at least ten times the size of the trade you plan to place.
Does high daily volume guarantee I can exit quickly?
No. High volume with falling open interest means traders are closing, not opening. You want both volume and open interest trending up or at least steady.
Should I ever accept a wide bid-ask spread?
Only if the premium you are collecting is large enough to absorb the slippage, and even then it is usually smarter to pick a different strike or a different expiration.
If you want the exact checklist I print out before every trade and the calculator that sizes the position for you, grab the mentorship at cashflowmachine.net/options-mentorship. The first lesson walks through a live liquidity screen so you can see the filters in action.
This is education, not financial advice. Past performance is not indicative of future results. Consult a qualified advisor before making investment decisions.