I’ve officially closed out two separate SPX Double Calendar/Diagonal trades today, March 18, 2026. Both walked away in the green after 10 trading days. The market stayed within my expected range, allowing theta to do the heavy lifting, but this morning provided a textbook lesson on the “mechanics” of trading versus the “strategy” of trading.

The Performance Breakdown

Trade 1: The “Wide” Diagonal (6625/6610 Puts & 7025 Calls)

This trade was a blend of a diagonal put spread and a calendar call spread.

• Initial Entry (Mar 4): Entered for a net debit of $6,846.44.
• The Exit (Mar 18): Closed for a net credit of $7,827.12.
• Total Net Profit: $980.68 (After Fees).
• Return on Risk: 14.3%

Trade 2: The “Narrow” Calendar (6680 Puts & 7000 Calls)

This was a tighter play centered on the 6680 and 7000 strikes.

• Initial Entry (Mar 4): Entered for a net debit of $7,001.44.
• The Exit (Mar 18): Closed for a net credit of $7,863.28.
• Total Net Profit: $861.84 (After Fees).
• Return on Risk: 12.3%

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The $1,000 “GTC” Mistake

While I’m happy with a total profit of $1,842.52 across both positions, it should have been closer to $3,000.

I made a classic execution error: I was attempting to close these trades yesterday but mistakenly left Good ‘Til Canceled (GTC) orders active instead of Good ‘Til Day (GTD). Because of this, the orders sat in the system overnight. When the market popped at the open this morning, those GTC orders triggered immediately.

Because they filled right at the bell, the prices were significantly lower than what I could have captured just a few minutes later as the underlying continued to trend favorably. I estimate I left about $1,000 on the table simply because of a dropdown menu choice on my order entry screen.

Closing Thoughts

Even with the execution hiccup, these trades were solid wins. While I could have held these closer to the front-month (March 19) expiration to squeeze out more decay, the gamma risk was starting to rise as we got within 24 hours of expiration. I’m happy to take my chips off the table.

This trade is a great reminder that even when your market thesis is 100% correct, disciplined order management is the final hurdle to a successful trade. Getting out before the Greeks get messy is the strategy—making sure your orders behave is the craft.