A Bull Call Spread Can Have Positive Theta

A Bull Call Spread Can Have Positive Theta

By Options Matrix Pro Editorial Team | Prepared 16 October 2026

A fictional $100/$110 bull call spread has a model value of $956.51 for one contract pair. One calendar day later, with the underlying price and every other pricing input unchanged, its value rises to $958.92. Both calls have lost value. The short call has lost more, so the difference between them has increased.

That result can occur even though the spread costs money to open. The opening debit records the price paid for the position. Theta estimates how its value responds to time passing from its current state. A debit alone cannot establish the sign of that sensitivity.

Combine the two legs with their position signs

A bull call spread owns a lower-strike call and owes a higher-strike call on the same underlying with the same expiration. Its value is the long call's value minus the short call's value. The vertical-spreads lesson explains the construction and expiration boundaries.

Use the same subtraction for theta. If a screen supplies each option's theta from the perspective of owning that option, then:

Net spread theta = lower-strike call theta minus higher-strike call theta.

Both individual calls can have negative theta. Subtracting the short call's negative theta makes a positive contribution to the position. The balance depends on which call is losing theoretical value faster. If a broker already displays position-signed Greeks, add those displayed contributions instead; reversing the short sign twice gives the wrong result.

The Options Industry Council's theta guide defines the estimate with other pricing factors held fixed and explains that decay is nonlinear. Confirm the screen's units too. A per-share daily theta must be multiplied by the contract multiplier and quantity to obtain the position's dollar sensitivity. A figure already expressed in position dollars needs no second multiplication.

Moving the underlying changes the time effect

The bull call spread guide published by Fidelity and credited to the CBOE Options Institute describes opposing time effects near the two strikes. Near the lower strike, the owned call can decay faster. Near or above the higher strike, the owed call can decay faster, helping the spread's value when other inputs stay fixed.

The following model makes that distinction measurable. It uses one hypothetical European-style $100 call bought and one $110 call sold, each with a multiplier of 100. Both have 30 calendar days remaining. Annualised volatility is fixed at 25%, interest and dividend rates are zero, and time is measured as calendar days divided by 365. No fees, taxes, spread, early exercise or position changes enter the calculation. All money figures are U.S. dollars.

These are invented model inputs, not quotes for a named stock or a claim that a particular listed equity option has European exercise. The OIC's Black-Scholes explanation identifies the pricing inputs and cautions that formulas do not determine executable premiums. This example isolates time using that model.

Upper-price state, 30 days remaining. Underlying $120; owned $100 call value $20.0137 per share; owed $110 call value $10.4487 per share; net spread value $9.5651 per share, or $956.51 for the pair. The owned call's daily theta is approximately -0.002052 per share. The owed call contributes +0.026187 per share after its position sign. Net daily theta is approximately +0.024135 per share, or +$2.41 for the pair.

Upper-price state, 29 days remaining. Underlying still $120; owned call value $20.0118; owed call value $10.4226; net spread value $9.5892 per share, or $958.92 for the pair. Repricing both legs gives a one-day value increase of $2.41. The owned call declines by about $0.20 per contract while the liability on the owed call declines by about $2.61.

Lower-price state, 30 days remaining. Underlying $100; owned $100 call value $2.8587 per share; owed $110 call value $0.3210 per share; net spread value $2.5377 per share, or $253.77 for the pair. The owned call's daily theta is approximately -0.047625 per share, and the short contribution is +0.020632. Net daily theta is approximately -0.026993 per share, or -$2.70 for the pair.

Lower-price state, 29 days remaining. Underlying still $100; owned call value $2.8107; owed call value $0.3005; net spread value $2.5102 per share, or $251.02 for the pair. The time-only value change is -$2.75.

The two starting states are alternative valuations of the same strikes, not two trades entered at the same debit. Calculations use unrounded values; each displayed figure is then rounded separately. The daily theta estimate and the full one-day reprice differ slightly because theta changes during the interval.

At $120, the short call is closer to the underlying price than the long call. It carries more time value and loses more of it in this model. At $100, the owned call is at the money and its decay dominates. The original payment direction has stayed the same in both states: each spread still has a positive value and would require a debit to acquire at its model price.

A favourable theta can sit beside a large loss

Suppose the upper-price spread was acquired at its unrounded model value, approximately $956.51, in a frictionless hypothetical transaction. One day later, let the underlying fall from $120 to $110 while volatility, rates and dividends remain unchanged. The spread's 29-day model value is then $720.87. The change from the original cost is a $235.63 loss before costs.

That scenario changes price as well as time. It cannot be described as a theta-only result. Nor can the initial +$2.41 estimate be subtracted from the total to produce a precise attribution: the legs' sensitivities change as the underlying moves. Reprice the full position under each stated scenario. The options-Greeks lesson treats these sensitivities as changing estimates rather than forecasts.

The high initial debit also leaves little remaining expiration upside. For the intact $100/$110 spread bought at that model cost, the greatest combined intrinsic value at expiration is $1,000. Maximum expiration profit is therefore $43.49 before costs. If both calls finish worthless, the option loss is $956.51. Positive theta neither enlarges that $43.49 ceiling nor removes the possibility of losing the full debit.

The OIC bull call spread reference gives the width-minus-debit profit formula and warns that the investment has a deadline. A favourable local time sensitivity can coexist with that deadline and a poor outcome. No daily theta amount is deposited into the account.

Real contracts add execution and assignment decisions

A theoretical increase becomes a trading result only through the position's actual closing or settlement path. A wider bid-ask spread, fees or an unfavourable fill can absorb a small model gain. The OIC's bid-ask explanation describes slippage and the possibility that a limit order will not execute. Review both legs and the net order, using the liquidity guide for the distinction between a displayed value and a fill.

The model's European exercise assumption also leaves out an important operational risk. OCC's equity-option specifications describe standard U.S. equity options as 100-share, American-style contracts, with stock delivery on exercise or assignment and T+1 exercise settlement. Adjusted contracts can have different deliverables. These terms must be checked for the actual series.

An American-style short call can be assigned before expiration. Owning the lower-strike call does not automatically exercise it in response. FINRA's assignment guidance explains that a spread holder may need to act on the remaining leg and meet the delivery obligation despite the original combined risk profile. Assignment can leave short shares, funding or margin requirements, and exposure between transactions. Expiration near a strike adds uncertainty about which options become stock positions. The intact expiration payoff calculation does not cap losses on an unmanaged stock position left afterwards.

Options involve risk and are not suitable for all investors. This is general education, not personal financial, legal or tax advice. Hypothetical premiums are not executable offers, and transaction costs and tax treatment can change net results. Read the current OCC options disclosure document and establish the broker's exercise, assignment, settlement and funding procedures before relying on a spread analysis. A small daily sensitivity does not establish that a position is affordable or appropriately sized.

Options Matrix Pro publishes this education and has a commercial interest in its research platform. The linked OMP lessons are first-party educational material; this example makes no claim about a broker's or OMP's current Greek-display convention. Our editorial policy explains the publishing standards.

Before interpreting a positive theta figure, write down the two signed leg contributions, their units and their common valuation time. Then reprice the complete spread one day later with other inputs fixed, and separately test an adverse underlying move. Keep the resulting loss and assignment-funding requirements beside the daily estimate.