Double Diagonal: Two Time Spreads with Different Strikes

For educational purposes only; not investment advice.

Direct answer

A double diagonal combines a put diagonal below the market and a call diagonal above it. A common structure sells a nearer-dated put and call at inner strikes while buying later-dated put and call protection at farther-out strikes. Each side differs in both strike and expiration, so the four-leg package is sensitive to price range, time decay, volatility term structure, and skew.

It is not a double calendar because corresponding strikes differ, and it is not an iron condor because the long and short legs expire on different dates. Its front-expiration value includes the market value of the surviving back options, so a one-expiration payoff chart cannot describe the full position.

Structure and lifecycle

With front expiration T₁ and back expiration T₂, one neutral example is:

Sell a 95/T₁ put and buy a 90/T₂ put.
Sell a 105/T₁ call and buy a 110/T₂ call.

The inner short strikes define the initial range, while the outer long options provide later-dated tail protection. The structure may open for a debit or credit depending on strikes, maturities, surfaces, rates, and dividends. Net Theta and Vega can change sign; the nearer shorts often decay faster, but the later longs can lose from falling implied volatility.

At T₁, the trader may close all legs, buy back the shorts and keep the back strangle, or roll the shorts. If a short option is assigned, the back option is not automatically exercised. Because its strike is farther out and it retains time value, reflexively exercising it can realize the strike gap and destroy extrinsic value.

Four-leg example

Assume the stock is $100:

Sell a 30-day $95 put for $1.40 and a 30-day $105 call for $1.30.
Buy a 90-day $90 put for $1.80 and a 90-day $110 call for $1.70.

The package costs a net $0.80 per share, or $80 with a 100-share multiplier.

At the front expiration, suppose the stock is $100, both shorts expire worthless, and the back put and call are worth $0.60 and $0.70. The package is worth $130, an illustrative $50 gain before costs. Those back-option values depend on remaining time and volatility and are not guaranteed.

If the stock finishes at $110, the short $105 call has $5.00 intrinsic value. Assume the back $110 call is worth $3.20 and the back put $0.10; net package value is $3.20+$0.10−$5.00=−$1.70. Relative to the $0.80 debit, that is an illustrative $250 loss before costs. The later call still has time value, so exercising it immediately at $110 to satisfy a $105 assignment would lock in a $5 strike gap and discard that value.

For an intact equal-ratio debit structure, a rough contractual extreme can resemble outer-to-inner strike width plus the debit. That is not a reliable account-level maximum: unequal wings, credits, legging, early assignment, adjusted deliverables, transaction costs, financing, and forced liquidation alter the realized result and cash requirement.

Risk checklist

Use a four-leg complex limit order where possible and verify the quoted net debit or credit.
Confirm every strike, expiration, option type, quantity, multiplier, settlement style, and deliverable.
Revalue the back options across spot, volatility, skew, and remaining-time scenarios at T₁.
Stress breaks below the short put and above the short call, including gaps through the long strikes.
Track American-style assignment, especially short calls before ex-dividend dates and deep-in-the-money puts.
Do not assume the broker will exercise or sell a back option to manage assigned stock.
Compare closing the back option with exercising it; exercise forfeits remaining extrinsic value.
Treat every roll as the close of an old position and opening of a new expiration risk.
Include four-leg spreads, commissions, financing, borrow, tax, margin, and after-hours exposure.

Common misconceptions

“It is just an iron condor.” Different expirations make value and risk path-dependent.
“It is a double calendar.” A double diagonal also changes strikes on each side.
“The long wings automatically cover assignment.” Broker actions and option exercise require separate instructions.
“Farther wings always make the trade cheaper and safer.” They reduce immediate premium but increase strike-gap exposure.
“Positive Theta pays the debit.” Theta is model-derived and can be outweighed by spot and volatility changes.
“A roll repairs the original trade.” It realizes the old result and creates a new position.