Bull call spread: time is a friend or an enemy depending on the midpoint
Use the time-slice chart to see the same spread at $100, $105, and $110, where time takes money, barely matters, and pays you.
All figures are Black-Scholes model estimates, not market quotes or guarantees.
US stock and ETF options are American-style and can be exercised at any time. This model treats every option as European and does not model early exercise or assignment.
P&L by price and day (model estimate, current price 100, IV 30%, 30 days)
| Underlying price | Day 0 | Day 7.5 | Day 15 | Day 22.5 | Day 27 | Day 30 |
|---|---|---|---|---|---|---|
| 95 | −$160 | −$190 | −$226 | −$269 | −$290 | −$294 |
| 100 | $0 | −$24 | −$60 | −$120 | −$183 | −$294 |
| 105 | +$205 | +$205 | +$206 | +$208 | +$208 | +$206 |
| 110 | +$401 | +$425 | +$462 | +$523 | +$589 | +$706 |
| 115 | +$546 | +$578 | +$619 | +$669 | +$700 | +$706 |
Structure and P&L at expiration: a short call buys a lower cost
A bull call spread has two legs: you buy a call with a strike of 100 and sell a call with a strike of 110, both expiring in 30 days. Every number on this page assumes a current price of $100, implied volatility (IV) of 30%, a 4% risk-free rate, no dividends, 30 days to expiration, and one contract per leg.
The 100 call costs $3.59 a share and the 110 call brings in $0.66, for a net debit of $293.59, against $359.11 for the long call alone.
- Max profit: $706.41, at $110 or above: the $1,000 width less the net debit.
- Max loss: $293.59, at $100 or below.
- Breakeven: $102.94.
The long 100 call covers the short 110 call, so there is usually no extra margin, though your broker has to approve spreads. At entry, Delta is +38.01 and the instantaneous Theta is −$2.71 a day, less than half the long call’s −$6.24.
Time profile: five prices, six points in time
The table above shows three distinct behaviors:
- At $100, time costs money every day. The spread loses the full $294, and 59% of that loss lands in the last 7.5 days.
- At $105, time hardly matters. The P&L stays between +$205 and +$208 for the whole 30 days and ends at +$206.
- At $110, time pays. The P&L climbs from +$401 to +$706, with 60% of the gain in the last 7.5 days.
The outer rows follow the same pattern with less force: $95 slides from −$160 to −$294, and $115 rises from +$546 to +$706.
The midpoint rule: why the time-neutral price stays near $105
The time-neutral price, where the next-day change switches sign, is $104.83 on day 0, $104.91 on day 15, and $105.03 on day 27. It moves noticeably only on the last day, to $106.42 with 1 day left.
Below the midpoint, the long 100 call holds more time value than the short 110 call, so the passing days cost you more than they return. Above it, the short call holds more, so each day pays you. Near $105 the two are about equal and cancel out, which is why the line sits close to the midpoint of the strikes.
Breakeven is not the time-neutral price ($102.94 vs. $104.83)
The breakeven answers “does the spread make money at expiration?” The time-neutral price answers “is time helping right now?” Between the two, the answers disagree.
At $104, the spread is profitable at expiration, +$106. But it shows +$163 on day 0 and +$150 on day 15: time is shrinking the gain the whole way, even though the trade ends in profit.
The last week: both sides speed up
At $100, instantaneous Theta goes from −$2.71 a day on day 0 to −$10.89 on day 22.5 and −$31.87 with 1 day left. At $110 the same thing happens in the other direction, reaching +$33.96 a day with 1 day left.
Over the last 3 days, the $100 line loses $110 and the $110 line gains $118. The time-neutral price jumps to $106.42 with 1 day left and keeps moving toward the 110 strike.
Try it in the Lab: three experiments
Drag the day slider toward expiration (the link opens on day 27) and watch the $100 and $110 lines spread apart: $0 and +$401 on day 0, −$183 and +$589 on day 27.
Open in the LabOn the time-effect map, find the time-neutral line near $105. Until about 3 days before expiration it barely moves; on the last day (the cursor is on day 29) it sits at $106.42 and bends toward the 110 strike.
Open in the LabMove the short leg’s strike to 105. The time-neutral line follows the new midpoint, to about $102.37 on day 0. Try 115 as well: the line moves to about $107.27.
Open in the Lab
Three common misconceptions
MisconceptionOnce the price reaches the short strike of 110, you have max profit.
What the numbers showA rise to $110 on day 0 shows only +$401. The +$706 comes at expiration, and 60% of the remaining gain arrives in the last 7.5 days.
MisconceptionThe two legs offset each other, so the spread barely feels time.
What the numbers showThat holds only near the midpoint. At $100 the spread still loses the full $294, 59% of it in the last 7.5 days.
MisconceptionPast breakeven, time is on your side.
What the numbers showThe breakeven is $102.94, but the time-neutral price is $104.83. At $104 the spread still shows +$106 at expiration, yet that gain shrinks all the way from +$163 on day 0.