Credit Spread Calculator

A credit spread calculator works out the maximum profit, maximum loss, break-even price, and risk/reward ratio for a vertical options credit spread strategy. It is used by options traders seeking defined-risk income strategies in neutral to directional market conditions.

How to Use the Credit Spread Calculator

1. Choose the spread type: bull put spread (bullish or neutral) or bear call spread (bearish or neutral).
2. Enter the strike price of the option sold.
3. Enter the strike price of the option bought.
4. Enter the premium received for the option sold and the premium paid for the option bought.
5. Enter the number of contracts (each contract covers 100 shares).
6. Click calculate to see the net credit, maximum profit, maximum loss, break-even, and return on risk.

The Formula

Net credit per share = Premium received (short option) - Premium paid (long option)

Maximum profit = Net credit x 100 x Number of contracts

Maximum loss = (Spread width - Net credit) x 100 x Number of contracts

Where spread width = |Strike sold - Strike bought|

Break-even for bull put spread = Short put strike - Net credit per share

Break-even for bear call spread = Short call strike + Net credit per share

Return on risk = Maximum profit / Maximum loss x 100

Real-World Example

Bull put spread on Stock XYZ trading at £55:

Sell 1 put at £50 strike for £1.80 premium. Buy 1 put at £47 strike for £0.70 premium.

• Net credit: £1.80 - £0.70 = £1.10 per share
• Total credit received: £1.10 x 100 = £110
• Spread width: £50 - £47 = £3
• Maximum profit: £110 (if stock closes above £50 at expiry)
• Maximum loss: (£3.00 - £1.10) x 100 = £190 (if stock closes below £47 at expiry)
• Break-even: £50 - £1.10 = £48.90
• Return on risk: £110 / £190 = 57.9%

The trade profits if the stock stays above £48.90 at expiry. The stock can fall nearly 11% from current levels (£55 to £48.90) and the position still breaks even.

Why Traders Use Credit Spreads

A credit spread (also called a vertical spread) has several advantages over naked options selling. Defined risk: unlike selling a naked put, which has substantial loss potential if the stock falls sharply, the long option in a credit spread caps the maximum loss at the spread width minus the credit received. Lower margin requirements: the defined maximum loss means brokers typically require lower margin than for uncovered options. Probability of profit: credit spreads can be structured with the break-even point well away from the current price, creating a high probability of the trade expiring profitable. For example, a bull put spread with a break-even 10% below the current price profits on any outcome except a large decline. The trade-off is that the income received (credit) is lower than a naked option, and the position still loses money in adverse scenarios.

Frequently Asked Questions

What is the difference between a bull put spread and a bear call spread? Both are credit spreads but with opposite directional bias. A bull put spread (selling a put and buying a lower-strike put) collects credit and profits if the underlying stays flat or rises. A bear call spread (selling a call and buying a higher-strike call) collects credit and profits if the underlying stays flat or falls. Both have limited profit (the credit received) and limited loss (the spread width minus the credit). They are mirror images of each other in terms of structure and risk.

When should I close a credit spread before expiry? Many traders close credit spreads when they have captured 50 to 75% of the maximum profit, rather than holding to expiry. Closing early reduces the risk of a late reversal turning a profitable trade into a loss and frees up capital for new trades. The remaining profit potential in the last few days before expiry is typically small relative to the continued risk of assignment or adverse moves. Conversely, if the spread moves against you (the short strike is tested), closing early limits the loss to less than the maximum.

What does implied volatility have to do with credit spreads? Credit spreads are short-volatility strategies: they profit when implied volatility falls or when the underlying stays within a range. Higher implied volatility inflates option premiums, allowing you to collect a larger credit for the same spread width. Traders often look to sell credit spreads when implied volatility is high (for example, before earnings or during periods of market uncertainty) to collect inflated premiums and benefit from the subsequent volatility contraction. Low-volatility environments produce smaller credits and less attractive risk/reward ratios.

Can I be assigned early on a credit spread? Early assignment is possible on American-style options (most US equity options) but less common on European-style options (most index options). In a bull put spread, early assignment occurs on the short put when it is deep in the money, particularly just before an ex-dividend date. If assigned early, you now own shares (from the put assignment) and still hold the long put hedge. The long put protects the position, but the dynamics change and you may need to exercise the long put or close the position. Early assignment risk is one reason many traders prefer cash-settled index options for credit spread strategies.

Also try these free tools:

• Covered Call Calculator
• Cash-Secured Put Calculator
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The other direction: a bear call spread

The example above is a bull put spread, which collects credit and profits when the underlying holds up. The mirror structure is a bear call spread, which collects credit and profits when the underlying holds down or stays flat. It runs on the same arithmetic.

A share trades at 100 pounds. The trader sells one call with a strike of 105 pounds for 2.40 pounds and buys one call with a strike of 110 pounds for 1.10 pounds, both expiring on the same date.

• Net credit per share: 2.40 minus 1.10 = 1.30 pounds.
• Total credit received: 1.30 times 100 = 130 pounds.
• Spread width: 110 minus 105 = 5.00 pounds, so 500 pounds of value per contract.
• Maximum profit: 130 pounds, kept if the share closes at or below 105 pounds at expiry.
• Maximum loss: (5.00 minus 1.30) times 100 = 370 pounds, taken if the share closes at or above 110 pounds.
• Break-even: 105 plus 1.30 = 106.30 pounds.
• Return on risk: 130 divided by 370 = 35.14 percent.

The trader keeps the full credit as long as the share does not rise past 105 pounds, which is 5 percent above the current price. The position breaks even at 106.30 pounds, so there is 6.30 pounds of room above the spot price before the trade starts losing. Past 110 pounds the loss stops growing, because the long call rises in value at the same rate as the short call.

The two structures side by side

Both examples use the same building blocks, and putting them in one table shows how differently the same credit translates into risk.

The bull put collects a smaller credit but sits much further from its break-even, 11.09 percent below the spot price against 6.30 percent above it for the bear call. That distance is the practical difference between the two trades, and it is bought with the return on risk: the bull put returns 57.89 percent on the capital at risk, the bear call 35.14 percent. A wider buffer and a higher return on risk do not usually arrive together, and when they do the difference is usually hiding in the distance between the two strikes.

Outcomes at expiry for both positions

A credit spread has three zones: a flat region where the full credit is kept, a sloped region between the two strikes, and a floor where the loss stops growing. The tables hold each position constant and move only the underlying price at expiry, with no time value left in either option.

Bear call spread, credit 130, break-even 106.30, maximum loss 370:

Bull put spread, credit 110, break-even 48.90, maximum loss 190:

The symmetry is the point. In the bear call the profit is flat below 105 and the loss is flat above 110, with the whole outcome decided in a 5 pound band. In the bull put the profit is flat above 50 and the loss is flat below 47, with the outcome decided in a 3 pound band. Everything that happens outside those bands changes nothing about the trade.

How the spread width changes the return on risk

Widening the spread buys more credit and takes on more risk, and the two do not move in proportion. The table holds the bull put credit fixed at 1.10 pounds per share and widens the distance between the strikes.

Going from a 3 pound width to a 5 pound width raises the capital at risk from 190 pounds to 390 pounds and leaves the profit unchanged at 110 pounds, which cuts the return on risk by more than half, from 57.89 percent to 28.21 percent. A wider spread is not a bigger trade; it is the same trade with more money on the line for the same reward, unless the credit also rises.

What a credit spread does not protect against

Defined risk stops the loss at a known number, and that is the main attraction. Four risks remain.

• A gap move overnight or over a weekend can take the underlying straight through both strikes before either option can be traded. The loss is still capped, but it arrives in one step rather than developing.
• Early assignment on the short leg is possible on American-style options, particularly when the short option is deep in the money near a dividend date. The long leg still caps the risk, and the mechanics of the position change once shares are delivered.
• Liquidity in the long leg is normally thinner than in the short leg. A wide quoted spread on the protective option reduces the net credit and makes the position harder to close early.
• The credit is small relative to the risk by construction. The maximum profit is the credit on a position that ties up the spread width minus the credit as capital, so a single loss can erase several wins.

What the spread figures assume

Six conditions sit behind the numbers above.

• The payoff tables value each option at intrinsic value at expiry. Time value is assumed to have run to zero, which is what happens at expiry and not what happens before it.
• Both legs are held to expiry. Many traders close a credit spread once 50 to 75 percent of the maximum profit has been captured, which changes the realised return and cuts the time the position is exposed.
• The long option is carried as a hedge and is not assumed to be exercised early.
• Commissions, exchange fees and the bid-ask spread are excluded. Credit spreads are short-premium positions, so transaction costs take a larger share of the profit than they do on a directional trade of the same size.
• Margin requirements are set by the exchange and the broker. A defined-risk spread attracts a lower requirement than the short option alone, because the long leg caps the maximum loss at the width minus the credit.
• The position is shown for one contract per leg, with each contract covering 100 shares.

One further note on the cash flow. The credit is received when the spread is opened, and the maximum loss is the amount that would have to be paid to close the position at the worst outcome. Capital at risk means the width minus the credit, not the full width, and not the credit itself.

Why the structure is defined risk

The payoff of a credit spread is the sum of a short option and a long option at a further strike, and the defined-risk property follows directly from that combination rather than from any special rule. The standard treatment of option payoffs and vertical spreads is in John C. Hull, Options, Futures, and Other Derivatives. For American-style equity options the assignment process and the margin treatment of a spread are set by the exchange and the broker rather than by the strategy itself, which is why the same spread can carry a different requirement on two accounts.