Why Friday-Monday calendars are a trap
Something I've stopped doing recently: Friday-Monday calendar spreads.
Sell a Friday. Buy the following Monday. On the retail platforms, the PNL projection looks great. In reality the trade almost always underperforms what the model promised.
Here's why.
Most retail platforms use a calendar-day theta model. When you look at a Friday-Monday calendar, the platform sees three days between the two expiries. Friday, Saturday, Sunday. The projected theta pickup assumes those three days of decay all show up.
The market runs on a business-day model. Between Friday close and Monday open, there's exactly one business day of decay.
That mismatch is where the trade gets you.
Because dealers know exactly one business day of decay is coming, they mark implied vol on Monday-expiry options down on Friday afternoon. They aren't going to pay you for two weekend calendar days that don't exist in trading time. If you're long the Monday, you get hit with that markdown right when the platform was projecting your peak theta payoff.
Unless there's a real event risk over the weekend (which there was during the height of the war), that vol markdown is basically guaranteed. Some major geopolitical event, an emergency Fed meeting, real macro news pending. Without that, the surface prices in what it knows.
You end up in a trade where the platform said you'd earn X, and the reality of Friday's mark strips out most of it. The model shown to you was built on the wrong day count.
The fix is straightforward.
Put distance between the expiries. A Friday-Wednesday calendar or a Friday-Friday calendar has enough business days between the legs that the theta model becomes far more accurate. The weekend markdown effect gets diluted into a longer decay window.
Or run the trade on a proper business-day model that already accounts for the weekend gap.
Remember: The framework I built across 20 years on bank options desks is below.
The bigger lesson extends past Friday-Monday calendars.
Any theta trade priced on a calendar-day model over a weekend, holiday, or long break is going to underdeliver relative to the platform projection. The market only pays theta for business days. Vol gets marked down for the ones it isn't going to charge you for.
If you can see that mismatch before you put the trade on, you either avoid it or size it correctly. The traders who get caught by weekend theta are usually looking at a platform model that treats the weekend like normal trading days. The Friday mark is when the fiction gets corrected.
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Imran
Disclaimer (Your Gains & Losses, Your Responsibility): This content from Options Insight LLC (“Options Insight”) is for educational purposes only and does not provide individual investment advice or recommendations, nor should it be considered an offer to buy or sell any security. All information is general and not tailored to your specific objectives, financial situation, or risk tolerance. Employees of Options Insight may hold positions in the assets discussed. While we use sources believed to be reliable, we are not responsible for errors, omissions, or losses resulting from reliance on this content. Always consult a licensed investment professional.
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