Credit Spread Calculator

A credit spread calculator turns the four numbers you see on your broker's option chain into the six numbers that actually decide whether a trade is worth taking: max profit, max loss, breakeven, return on risk, estimated probability of profit, and spread width. A credit spread is a two-leg options position where you sell one option and buy another option of the same type (both puts or both calls) and the same expiration, collecting more premium (the upfront price of an option) from the option you sell than you pay for the option you buy. That difference is your net credit, and it is the most you can ever make. Because you also own a further-away option as protection, your loss is capped, which is what makes a credit spread a defined-risk strategy. The calculator above runs these numbers instantly so you can size the trade before you click, not after. Options can and often do expire worthless, so treat every output as a risk map, not a profit promise. Nothing here is financial or tax advice.

What Is a Credit Spread?

A credit spread, also called a vertical credit spread, is built from two options of the same type and the same expiration date but different strike prices. You sell the option that is closer to the current price (the short leg) and buy the option that is further away (the long leg). Selling the closer option brings in more money than buying the further one costs, so cash lands in your account on day one. That net cash is the credit. Your goal is for both options to lose value or expire worthless so you keep as much of that credit as possible.

There are two kinds. A put credit spread (sometimes called a bull put spread) is a bullish bet: you sell a put at a higher strike and buy a put at a lower strike, and you profit as long as the underlying stays above your short strike. A call credit spread (a bear call spread) is a bearish bet: you sell a call at a lower strike and buy a call at a higher strike, and you profit as long as the underlying stays below your short strike. In both cases the long leg you bought is insurance that caps the damage if the trade goes against you.

Defined Risk vs Naked Selling

Selling an option on its own, with no protective long leg, is called naked selling. A naked put can lose money all the way down to a stock price of zero, and a naked call carries theoretically unlimited risk because a stock can keep rising with no ceiling. A credit spread removes that open-ended danger. The long leg you buy sets a hard floor under the loss, so the most you can lose is the distance between the two strikes minus the credit you collected. That is why brokers require far less margin for a spread than for a naked short. You trade away some premium (the long leg costs money) in exchange for a known, capped, sleep-at-night worst case.

What the Credit Spread Calculator Does

The calculator above takes five inputs and returns six outputs. The inputs describe the exact spread you are looking at on the chain. Spread Type tells the tool whether you are running a put credit spread (bullish) or a call credit spread (bearish), which controls how breakeven is calculated. Short Strike is the strike of the option you sell, the leg closer to the current price. Long Strike is the strike of the protective option you buy, further from the price. Net Credit is the total premium per share you collect after subtracting what the long leg costs, for example 1.50 if you sell for 2.10 and buy for 0.60. Contracts is how many spreads you are trading, where each contract controls 100 shares.

From those, the outputs are: Spread Width, the dollar distance between the two strikes; Max Profit, the credit kept if both options expire worthless; Max Loss, the capped worst case; Breakeven, the underlying price where the trade neither makes nor loses money at expiration; Return on Risk, the max profit divided by the max loss expressed as a percentage; and Estimated POP, a rough probability that the trade finishes profitable. Each output is explained with a formula in the next sections so you know exactly where the number came from.

How to Use the Credit Spread Calculator

1. Pick your direction. Choose put credit if you are mildly bullish (expecting the underlying to hold or rise) or call credit if you are mildly bearish (expecting it to hold or fall).
2. Enter the Short Strike. This is the strike you are selling, the leg nearer the current price. On a put credit spread it sits below price; on a call credit spread it sits above price.
3. Enter the Long Strike. This is the protective strike you are buying, further from the current price. The gap between the two sets your spread width.
4. Enter the Net Credit. Read it off the chain as the mid price of the sell leg minus the mid price of the buy leg, quoted per share (the calculator multiplies by 100 for you).
5. Enter the number of Contracts you intend to trade.
6. Read the outputs. Focus first on Max Loss, then check whether Return on Risk and Estimated POP fit your plan before you ever place the order.

The Formulas Behind the Calculator

The mechanics are simple arithmetic once you see them laid out. Every dollar figure is multiplied by 100 shares per contract and then by the number of contracts.

• Spread Width = the absolute difference between Short Strike and Long Strike (in points).
• Max Profit = Net Credit x 100 x Contracts. This is realized only if both legs finish worthless.
• Max Loss = (Spread Width minus Net Credit) x 100 x Contracts. This is the width you are exposed to, less the credit you already banked.
• Breakeven for a put credit spread = Short Strike minus Net Credit. Below this the trade loses.
• Breakeven for a call credit spread = Short Strike plus Net Credit. Above this the trade loses.
• Return on Risk = Max Profit divided by Max Loss, shown as a percentage.
• Estimated POP is approximated as 1 minus (Net Credit divided by Spread Width). It is a quick guide, not a guarantee, and it ignores volatility skew and dividends.

Notice the tension baked into these formulas. Collecting a bigger credit raises max profit and pulls breakeven closer to safety, but it also means you sold a strike nearer the money, which lowers estimated POP. Collecting a smaller credit raises POP but shrinks max profit while barely denting max loss, so return on risk falls. The calculator makes that trade-off visible instead of leaving it to gut feel.

Three Worked Examples

Example 1: Bullish Put Credit Spread on SPY

You are mildly bullish on SPY, the S&P 500 ETF, trading near 585. You sell the 580 put and buy the 575 put in the same expiration, collecting a net credit of 1.50 for one contract. Spread Width is 580 minus 575, which is 5 points. Max Profit is 1.50 x 100, which is 150 dollars. Max Loss is (5 minus 1.50) x 100, which is 350 dollars. Breakeven is 580 minus 1.50, which is 578.50, so SPY only needs to finish above 578.50 for the trade to be a winner. Return on Risk is 150 divided by 350, about 42.9 percent. Estimated POP is 1 minus (1.50 divided by 5), which is 70 percent. This is a balanced trade: a healthy return on risk paired with a solid but not extreme probability.

Example 2: Bearish Call Credit Spread on AAPL

You expect AAPL, trading near 226, to stall. You sell the 230 call and buy the 235 call, collecting a net credit of 1.20, and you trade two contracts. Spread Width is 235 minus 230, which is 5 points. Max Profit is 1.20 x 100 x 2, which is 240 dollars. Max Loss is (5 minus 1.20) x 100 x 2, which is 760 dollars. Breakeven is 230 plus 1.20, which is 231.20, so AAPL must finish below 231.20 for you to keep money. Return on Risk is 240 divided by 760, about 31.6 percent. Estimated POP is 1 minus (1.20 divided by 5), which is 76 percent. Trading two contracts doubles both the reward and the risk, which is exactly why the calculator scales max loss by contract count.

Example 3: The High-POP, Low-Return Trap on QQQ

You want a trade that almost always wins on QQQ, the Nasdaq-100 ETF, trading near 510. You sell a far put at 500 and buy the 495 put, collecting only 0.60 of credit for one contract. Spread Width is 5 points. Max Profit is 0.60 x 100, which is 60 dollars. Max Loss is (5 minus 0.60) x 100, which is 440 dollars. Breakeven is 499.40. Return on Risk is 60 divided by 440, just 13.6 percent. Estimated POP is 1 minus (0.60 divided by 5), which is 88 percent. The trade wins nearly nine times out of ten, but a single max loss of 440 dollars wipes out more than seven of your 60 dollar wins. This is the core lesson of credit spreads: a very high probability of profit almost always hides a punishing return on risk.

Credit Spread Reference Table

The table below shows how the outputs shift as you change the credit on a fixed 5-point-wide spread, one contract each. It makes the POP versus return on risk trade-off concrete. All figures assume the short strike is 580 on a put credit spread.

Read the table top to bottom and the pattern is unmistakable. The safest-looking row, 88 percent POP, pays the worst return on risk. The row with a coin-flip 50 percent POP pays a 1-to-1 return on risk. Neither is right or wrong; the point is that the calculator forces you to choose your spot on that curve on purpose rather than by accident.

Tips for Trading Credit Spreads With Discipline

• Size by max loss, not credit. Decide the most you will lose on one trade first, then let the calculator's Max Loss line tell you how many contracts fit.
• Consider closing at about 50 percent of max profit. Buying the spread back once it has captured half the credit locks in gains, frees margin, and removes the fat tail risk of holding into expiration.
• Mind assignment risk near expiration. If the short leg finishes in the money, or if it is a dividend-paying stock going ex-dividend, the short option can be exercised and you can be assigned shares.
• Match width to your account. A wider spread collects more credit but raises max loss point for point. Narrower spreads keep the worst case small.
• Avoid holding through binary events unless you mean to. Earnings, Fed meetings, and major economic data can gap price straight through both strikes.
• Log the plan and the exit rule before you enter, then compare the result to the plan afterward. That review loop is where the edge actually compounds.

Common Mistakes to Avoid

The most common error is judging a spread by its credit alone. A 2.00 credit feels good until you notice the max loss is 3.00 and the POP is only 60 percent. The second mistake is chasing very high POP trades, the 90 percent winners, without doing the arithmetic on how many wins one loss erases. The third is oversizing: because the credit lands in the account immediately, it is tempting to treat it as free money and stack too many contracts, so a single adverse move blows past a sensible daily loss limit.

Two more traps are worth naming. Traders often forget assignment and early-exercise risk, especially on individual stock names like AAPL rather than cash-settled index products; getting assigned 100 short shares per contract can be a nasty surprise if you are not watching. And many hold every spread to the last minute hoping to squeeze the final few dollars of credit, which is exactly when a small paper win can flip into a full max loss. If you are curious about the old 25,000 dollar Pattern Day Trader minimum, note that FINRA eliminated that requirement in June 2026, so it is no longer the barrier to frequent day trading it once was; it is not a current rule.

How This Supports Disciplined Journaling

A calculator tells you what a trade risks. A journal tells you whether your process is actually working. When you log a credit spread on OneTradeJournal, you can record the six outputs from the calculator alongside your reason for the direction, your planned exit at 50 percent, and what actually happened. Over dozens of trades that record answers the questions gut feel cannot: are your high-POP trades really profitable after the occasional max loss, is your breakeven cushion big enough, are you closing early when you said you would? Discipline-first trading is not about one clever spread; it is about repeating a rule you can measure. The calculator sets the rule for a single trade, and the journal proves whether the rule holds across many.

Run your next credit spread through the calculator above, note the max loss and return on risk, then log the trade on OneTradeJournal with your planned exit. Over time that simple habit, one calculated trade recorded honestly at a time, is what separates disciplined traders from hopeful ones.