By Matt Connor
How Many DTE for a Credit Spread?
How many DTE for a credit spread? We price one 5 wide put spread at 21 and 41 days, then compare credit per day, collateral, theta, and gamma at entry.
How many DTE for a credit spread has an arithmetic answer, and the arithmetic moves with every input you feed it. DTE is days to expiration: the calendar days between today and the day a contract stops trading. The useful comparison between two tenors measures credit per day of risk carried and credit per dollar of collateral tied up. Total credit on its own settles nothing, and this page prices one spread at two tenors to show why.
What is a credit spread, and what does DTE change?
A credit spread is a two-leg position. You sell one option and buy another of the same type and expiration further out of the money, and money comes into the account at entry, which is where the name comes from. The distance between the strikes is the width. For a put credit spread, the most the position can lose is the width minus the credit, and that same figure is the collateral a broker holds against it. The credit spread versus debit spread distinction sits entirely in that direction of cash flow at entry.
Hold the strikes and the width fixed and change only the expiration, and exactly one input moves: days to expiration. Every consequence of the tenor decision runs through it. Premium rises with more time. So does the number of days the stock has in which to reach the short strike.
How many DTE for a credit spread: two tenors priced
The example below is hypothetical and fully specified, so any reader can rebuild it. A stock sits at $100. Sell the 95 strike put, buy the 90 strike put, one contract of each, 5 points wide. Implied volatility is 25 percent and flat across both expirations. The risk-free rate is 4 percent, no dividends, European exercise. Prices and greeks come from the Black-Scholes formula. None of these figures is a quote from a live market. Delta and gamma are quoted per share; theta is in dollars per contract per day.
At 21 DTE:
- Credit: $51.08
- Credit per calendar day: $2.43
- Maximum loss and collateral: $448.92
- Credit as a share of collateral: 11.4 percent
- Breakeven at expiration: $94.49, or 5.51 percent below the stock
- Theta at entry: $2.48 per day
- Gamma at entry: -0.031
- Delta at entry: +0.144
At 41 DTE:
- Credit: $88.06
- Credit per calendar day: $2.15
- Maximum loss and collateral: $411.94
- Credit as a share of collateral: 21.4 percent
- Breakeven at expiration: $94.12, or 5.88 percent below the stock
- Theta at entry: $1.37 per day
- Gamma at entry: -0.018
- Delta at entry: +0.152
The exact SQL behind every number
WITH
100.0 AS spot,
95.0 AS short_strike,
90.0 AS long_strike,
0.25 AS iv,
0.04 AS rate,
100 AS contract_multiplier
SELECT
concat(toString(dte), ' DTE') AS tenor,
round(credit, 2) AS credit_usd,
round(credit / dte, 2) AS credit_per_day_usd,
round(collateral, 2) AS collateral_usd,
round(100 * credit / collateral, 1) AS credit_pct_of_collateral,
round(100 * credit / dte / collateral, 3) AS credit_per_day_pct_of_collateral,
round(breakeven, 2) AS breakeven_usd,
round(100 * (spot - breakeven) / spot, 2) AS breakeven_pct_below_spot
FROM
(
-- Position level: short the 95 put, long the 90 put, one contract each
SELECT
dte,
-sum(side * put_price) * contract_multiplier AS credit,
(short_strike - long_strike) * contract_multiplier - credit AS collateral,
short_strike - (credit / contract_multiplier) AS breakeven
FROM
(
-- Leg level: Black-Scholes put price, normal CDF built from erf()
SELECT
dte,
strike,
if(strike = short_strike, -1, 1) AS side,
dte / 365.0 AS t,
(log(spot / strike) + ((rate + ((iv * iv) / 2)) * t)) / (iv * sqrt(t)) AS d1,
d1 - (iv * sqrt(t)) AS d2,
0.5 * (1 + erf(-d1 / sqrt(2))) AS n_neg_d1,
0.5 * (1 + erf(-d2 / sqrt(2))) AS n_neg_d2,
(strike * exp(-rate * t) * n_neg_d2) - (spot * n_neg_d1) AS put_price
FROM (SELECT arrayJoin([21, 41]) AS dte) AS tenors
CROSS JOIN (SELECT arrayJoin([short_strike, long_strike]) AS strike) AS legs
)
GROUP BY dte
)
ORDER BY dteThe 41 day spread collects 72 percent more credit for 95 percent more calendar time. Premium scales closer to the square root of time than to time itself, and each additional day buys less than the day before it. That single fact produces the whole case for selling short-dated spreads.
The exact SQL behind every number
WITH
100.0 AS spot,
95.0 AS short_strike,
90.0 AS long_strike,
0.25 AS iv,
0.04 AS rate,
100 AS contract_multiplier
SELECT
concat(toString(dte), ' DTE') AS tenor,
round(credit, 2) AS credit_usd,
round(credit / dte, 2) AS credit_per_day_usd
FROM
(
SELECT
dte,
-sum(side * put_price) * contract_multiplier AS credit
FROM
(
SELECT
dte,
strike,
if(strike = short_strike, -1, 1) AS side,
dte / 365.0 AS t,
(log(spot / strike) + ((rate + ((iv * iv) / 2)) * t)) / (iv * sqrt(t)) AS d1,
d1 - (iv * sqrt(t)) AS d2,
0.5 * (1 + erf(-d1 / sqrt(2))) AS n_neg_d1,
0.5 * (1 + erf(-d2 / sqrt(2))) AS n_neg_d2,
(strike * exp(-rate * t) * n_neg_d2) - (spot * n_neg_d1) AS put_price
FROM (SELECT arrayJoin([21, 28, 35, 41, 45, 60, 75, 90]) AS dte) AS tenors
CROSS JOIN (SELECT arrayJoin([short_strike, long_strike]) AS strike) AS legs
)
GROUP BY dte
)
ORDER BY dteIs credit per day the right measure?
Per calendar day, the 21 day spread collects $2.43 and the 41 day spread collects $2.15, a 13 percent edge to the shorter tenor. Taken alone that number flatters the short tenor, since the two positions do not tie up the same money.
The larger credit on the 41 day spread shrinks its maximum loss, and the collateral falls with it: $411.94 against $448.92. Normalise each credit by the money at risk and the 21 day spread returns 0.542 percent of collateral per day, against 0.521 percent for the 41 day spread. The real edge is about 4 percent, well under the 13 percent the raw per-day figures suggest.
Running the 21 day spread twice covers 42 days, one more than the longer tenor, for $102.17 of gross credit against $88.06. Two entries also carry two sets of commissions and two crossings of the bid-ask spread, neither of which appears in the model above.
What the shorter tenor gives up
Gamma measures how fast delta changes as the stock moves. A credit spread seller is short gamma, meaning the position's directional exposure moves against the seller as the stock travels toward the short strike. Theta and gamma travel together as expiration approaches. See how option greeks change over time for the mechanics, and what option theta measures for the decay side on its own.
At entry the 21 day spread carries theta of $2.48 a day against $1.37 for the 41 day spread, 1.8 times as much. Its gamma is 1.7 times as large. The decay advantage and the convexity cost arrive in nearly the same proportion.
Drop the stock instantly to $95, the short strike, with no time passing. The 21 day spread marks at $164.62, a loss of $113.54, or 25.3 percent of collateral. The 41 day spread marks at $185.45, a loss of $97.39, or 23.6 percent of collateral. Measured against the credit collected, that same 5 percent move erases 2.2 times the credit on the 21 day spread and 1.1 times on the 41 day spread.
The exact SQL behind every number
WITH
100.0 AS spot_at_entry,
95.0 AS spot_after_drop,
95.0 AS short_strike,
90.0 AS long_strike,
0.25 AS iv,
0.04 AS rate,
100 AS contract_multiplier
SELECT
concat(toString(dte), ' DTE') AS tenor,
round(theta_share * contract_multiplier, 2) AS theta_usd_per_day,
round(gamma_share, 3) AS gamma_per_share,
round(delta_share, 3) AS delta_per_share,
round(mark_after_drop, 2) AS mark_after_drop_usd,
round(mark_after_drop - credit, 2) AS loss_usd,
round(100 * (mark_after_drop - credit) / collateral, 1) AS loss_pct_of_collateral,
round(delta_share * (spot_at_entry - spot_after_drop) * contract_multiplier, 2) AS delta_predicted_loss_usd,
round((mark_after_drop - credit)
- (delta_share * (spot_at_entry - spot_after_drop) * contract_multiplier), 2) AS gamma_share_of_loss_usd
FROM
(
-- Same position priced at both spots: entry at $100, then instantly at $95
SELECT
dte,
-sumIf(side * put_price, spot = spot_at_entry) * contract_multiplier AS credit,
(short_strike - long_strike) * contract_multiplier - credit AS collateral,
-sumIf(side * put_price, spot = spot_after_drop) * contract_multiplier AS mark_after_drop,
sumIf(side * put_theta_day, spot = spot_at_entry) AS theta_share,
sumIf(side * put_gamma, spot = spot_at_entry) AS gamma_share,
sumIf(side * put_delta, spot = spot_at_entry) AS delta_share
FROM
(
SELECT
dte,
strike,
spot,
if(strike = short_strike, -1, 1) AS side,
dte / 365.0 AS t,
(log(spot / strike) + ((rate + ((iv * iv) / 2)) * t)) / (iv * sqrt(t)) AS d1,
d1 - (iv * sqrt(t)) AS d2,
0.5 * (1 + erf(-d1 / sqrt(2))) AS n_neg_d1,
0.5 * (1 + erf(-d2 / sqrt(2))) AS n_neg_d2,
exp(-(d1 * d1) / 2) / sqrt(2 * pi()) AS pdf_d1,
(strike * exp(-rate * t) * n_neg_d2) - (spot * n_neg_d1) AS put_price,
-n_neg_d1 AS put_delta,
pdf_d1 / (spot * iv * sqrt(t)) AS put_gamma,
((-spot * pdf_d1 * iv / (2 * sqrt(t)))
+ (rate * strike * exp(-rate * t) * n_neg_d2)) / 365.0 AS put_theta_day
FROM (SELECT arrayJoin([21, 41]) AS dte) AS tenors
CROSS JOIN (SELECT arrayJoin([short_strike, long_strike]) AS strike) AS legs
CROSS JOIN (SELECT arrayJoin([spot_at_entry, spot_after_drop]) AS spot) AS spots
)
GROUP BY dte
)
ORDER BY dteDelta alone would have predicted a $71.92 loss on the shorter spread and $75.77 on the longer one. The extra damage, $41.62 against $21.62, is gamma. A given move consumes a larger share of a near-dated option's remaining time value, and the position's delta swings further per point of stock movement.
The expiration breakeven moves with the credit as well: $94.49 for the 21 day spread and $94.12 for the 41 day spread. The longer tenor buys 0.37 points more cushion, and hands the stock 20 more days in which to use it.
What the flat volatility assumption hides
The full assumption set behind every figure above
- Implied volatility flat at 25 percent across both expirations, with no term structure
- No skew: the 90 and 95 strikes carry identical implied volatility
- European exercise, with no early assignment on the short put
- No dividends and no commissions
- No bid-ask spread: every price is a theoretical mid
- Risk-free rate constant at 4 percent
- Prices and greeks from the Black-Scholes formula, theta quoted per calendar day
- Stock at $100, strikes at 95 and 90, one contract per leg
Real option chains rarely look like that. Volatility term structure usually slopes upward in quiet conditions, which lifts the longer tenor's premium above what a flat curve produces and narrows the shorter tenor's per-day edge. When the curve inverts ahead of a dated event, the near expiration carries the higher implied volatility and that edge widens instead. Put skew adds another layer: the 90 strike normally trades at a higher implied volatility than the 95, which makes the long leg dearer than this example assumes and trims the credit at both tenors. American-style equity options also carry early assignment risk on the short leg, which grows as the short put moves in the money and as an ex-dividend date approaches. Each of those effects has one remedy: replace the flat 25 percent with the implied volatility actually quoted at each strike and expiration, then re-run the same arithmetic.
Is 21 or 45 DTE a rule?
Neither is a rule. Both are conventions that circulate in options education alongside the 3-5-7 rule in options, and both are outputs of one particular set of inputs rather than properties of the market. Widen the spread from 5 points to 10 and the collateral ratio shifts. Raise volatility from 25 to 40 percent and both credits rise unevenly. Move the short strike from 5 percent out of the money to 2 percent and the gamma penalty at the near tenor grows sharply. Swap the put spread for a call spread and the skew works the other way. The comparison takes a short Black-Scholes function and a few lines of arithmetic, and it answers for your inputs rather than someone else's.
FAQ
What does DTE mean for a credit spread?
DTE is days to expiration: the calendar days between today and the contract's last trading day. For a credit spread it sets how much premium the position collects, how fast that premium decays, how sharply delta moves when the stock moves, and how much collateral the broker holds.
Does a shorter DTE credit spread collect more per day?
In the flat-volatility example above, yes: $2.43 a day at 21 DTE against $2.15 at 41 DTE. Measured per dollar of collateral the gap narrows to roughly 4 percent, and the shorter tenor carries about 1.7 times the gamma.
How much collateral does a credit spread tie up?
The width of the spread minus the credit received, multiplied by 100 for a standard contract. A 5 point put spread paying $88.06 of credit holds $411.94; the same width paying $51.08 holds $448.92. A larger credit lowers both the maximum loss and the collateral.
Why does gamma matter more at short DTE?
Gamma measures how fast delta changes. Near expiration, a given move consumes a larger share of the option's remaining time value, and delta swings further per point of stock movement. In the example above, a 5 percent drop cost the 21 day spread $41.62 beyond what delta predicted, against $21.62 for the 41 day spread.
Does implied volatility skew change the answer?
Yes. The example holds volatility flat at 25 percent across strikes and expirations. Real chains price the lower put strike at a higher implied volatility, and often price longer expirations above shorter ones. Both of those move the credit and the per-day comparison.
Every figure here follows from a stated set of inputs and a short Black-Scholes function, with nothing read off a live chain. Change the strikes, the width, the volatility, or the rate, and price the same comparison for your own numbers on the Strasmore terminal.