SPX Vertical Credit Spread — July 13, 2026: Iron-Condor Lattice on a Quiet Tape

Reasoning

Overnight, ES traded in a 12-point range with no overnight gap on SPX. Pre-market VIX came in at 11.4 — a quiet tape, low realized vol, and a Put/Call ratio running at 0.78 (slightly put-skewed but well within neutral).

The 5,560/5,545 short-put strike sat roughly 1.4% below the open. With 0DTE, the theta curve is steep and the gamma is concentrated at the strikes. That makes premium-to-width the right edge metric for 0DTE verticals — a 7% reading is on the lower end of the workable range for a quiet tape, but the calendar setup (no FOMC, no CPI, no earnings heavy-hitters) gave me comfort to take the trade at a smaller edge in exchange for the small max risk relative to the daily P&L goal.

The position is sized to a max loss of 0.15% of NLV (net liquidating value), well inside the playbook's 0.25% per-trade cap.

Position Payoff at Expiration

The P/L diagram for this trade is a textbook short put vertical. The structure has a flat region above the short strike (the full credit is kept), a sloped loss region between the short strike and the long strike (where intrinsic accumulates against the short leg), and a flat max-loss region below the long strike (where the long leg's intrinsic exactly offsets the short leg's loss).

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Key levels for this trade:

• Upper profit boundary — SPX at expiration above 5,560. The position keeps the full $1.05/share credit × 5 contracts = $525 max profit.
• Lower profit boundary — SPX at expiration exactly at 5,560. The short put is at-the-money; intrinsic is zero; the position keeps the full credit.
• Breakeven — SPX at 5,558.95 (short strike 5,560 minus credit $1.05). Below this point, the position starts to lose dollar-for-dollar with the underlying.
• Max loss — SPX at expiration below 5,545. The long put offsets the short put; the position locks at the width ($15) minus the credit ($1.05) = $13.95/share × 5 contracts × 100 multiplier = $6,975 realized max loss (notional) before the day's partial close.
• Realized max loss (worst case for this trade): the position was closed at the 50% profit target, so the realized max loss would have been the full $7,500 if SPX had gapped below 5,545 between the 11:14 test and the 1:32 close. That risk is part of why the position size is capped at 0.15% of NLV.

Greeks Snapshot (Black-Scholes)

Numbers computed at entry spot 5,575, 0 DTE, IV=11.2% (entry chain IV), r=4.5%, no dividend yield. Per-contract = per-share × 100.

Why This Structure

A put credit spread on SPX at 0DTE was the right structure for the day because:

• The view was directionally neutral but vol-constructive. Pre-market VIX at 11.4 was below the 25th percentile of the past year; realized vol had been tracking below 10% for the prior two weeks. The combination of low realized vol, low IV, and a quiet overnight tape reads as "the market will continue to chop, sell premium while it's cheap."
• The structure expresses the view with defined risk. A naked short put would have unbounded downside; the long 5,545 put caps risk at $15/contract × 100 × 5 contracts = $7,500. That's the worst-case loss if SPX gaps below 5,545 between entry and expiration.
• The width is sized to the day's expected move. The 5,560 short strike sat about 1.4% below the open. The 15-point width (to 5,545) gives a 1.0% lower buffer, which is consistent with the 30-day 1σ move for SPX at current IV (about 0.67% per day, or 1.5% per week).
• 0DTE is the right DTE for the edge. Theta at 0DTE is concentrated in the last 2-3 hours. A multi-day structure would have given up too much premium in time decay while waiting for the short strike to be tested.

Thesis

• Why sell premium at all when IV rank is 22? Because premium-to-width, not IV rank, is the right edge metric for 0DTE verticals. A 7% premium-to-width on a 0DTE SPX vertical is workable; a 4% reading is not. Today was at the lower bound.
• Why the 5,560/5,545 strikes? Roughly 1.4% below the open on the put side, which sits inside the day's expected-move range while keeping the credit-to-width ratio above the 5% threshold. A further OTM short strike (e.g., 5,540) would have improved the POP but cut the credit below 5%.
• Why only 5 contracts? Max-loss cap is 0.15% of NLV; the position respects the per-trade rule (0.25%) with comfortable headroom. Sizing is the most important defense against a 0DTE gap; capping at 0.15% keeps a 2× stop within the day's drawdown limit.
• Why exit at 50% of credit rather than hold to expiry? The playbook's first rule: take 50% of credit at 50% decay. At 0DTE, the second half of the credit decays faster, but the risk/reward of holding the second half is no longer asymmetric — you'd be risking another $0.40 to make another $0.50. Holding past 50% has positive expected value but lower Sharpe; closing at 50% is the higher-Sharpe move.

Risk

Management Plan

• Open through 11:30 AM ET: hold; position is working. Theta is the main driver. Watch for any sign of an intraday vol spike (a VIX move > 1 point, an unexpected macro headline).
• 11:30 AM – 1:00 PM ET: if premium has decayed 40%+ and SPX is above the short strike, take partial profits or close the full position at 50% of credit. The second half of the credit decays slower than the first, and the gamma-acceleration risk rises as time-to-expiry shrinks below 3 hours.
• 1:00 PM – 3:00 PM ET: prefer the close. The theta curve flattens in the last 90 minutes; the only way to lose meaningfully in that window is a directional gap, which is the unmodeled risk that the position size cap is designed to absorb.
• At or near 2× credit stop: close immediately. The structure is no longer expressing the original view (premium-to-width ratio has deteriorated below the threshold).

The realized exit was the 50% profit target at 1:32 PM, which is consistent with the playbook.

Intraday Management

• 11:14 AM ET: SPX tested 5,565, took the short strike within 5 points. No action — the position has positive gamma below the short strike, so further downside accelerates loss non-linearly but the 2× stop is the only management rule.
• 1:32 PM ET: SPX rebased to 5,572, premium decayed to $0.42 (a 60% decay). Took the 50% profit target. Closed the position for $0.42 buyback.

Outcome

A clean execution. The playbook's two rules — take 50% of credit at 50% decay, or close at 2× credit — are non-negotiable, and today the first rule fired cleanly. The remaining $0.63 of the spread was exercised/expired; since SPX settled at 5,578, both legs expired worthless.

Lessons

• The premium-to-width threshold for 0DTE verticals on a quiet tape is 5–8%. I would have passed on a 4% reading. Today sat at the lower bound of the workable range.
• Positive gamma below the short strike is real. From 11:14 onward, the position's delta-decay accelerated as SPX approached the strike, then flipped hard once we were inside. The 60% decay in two hours confirms the textbook gamma profile.
• The playbook's 0.15% NLV max-loss cap meant that even a 2× stop (the worst case) would have lost $0.30% of NLV. Well within the daily drawdown limit.

No trade tomorrow if VIX is below 10. The edge just isn't there.