Introductory Context
"The inverted trapezoid profile is the visual expression of the credit spread's economics: the strategy collects a small, certain income in exchange for accepting a defined but larger potential loss. The profile's asymmetry -- small profit zone, larger loss zone -- is what makes the credit spread a higher-probability but lower-reward-to-risk structure. Understanding this profile precisely is essential for correctly evaluating whether any specific bull put spread provides sufficient credit yield relative to its maximum risk. "
The Three Payoff Zones
Zone 1 -- Above the short put strike (above 22,500 in the Topic 13.10 example): both puts expire worthless. P&L = full credit received = Rs 2,475 per lot. This is the maximum profit zone. Regardless of how high Nifty rises above 22,500, the profit is flat at Rs 2,475.
Zone 2 -- Between the long and short put strikes (22,000 to 22,500): the short put is ITM (Nifty below the 22,500 strike) and the long put is OTM (Nifty above the 22,000 strike). P&L = [net credit - (short put intrinsic value)] x lot size. At Nifty 22,300: short put intrinsic = Rs 200. P&L = (33 - 200) x 75 = -Rs 12,525. The position is in loss below the 22,467 break-even.
Zone 3 -- Below the long put strike (below 22,000): both puts are ITM. The long put's gain exactly offsets the short put's obligation beyond the spread width. P&L = [net credit - spread width] x lot size = [33 - 500] x 75 = -Rs 35,025. This is the maximum loss -- fixed regardless of how far below 22,000 Nifty falls. The long put provides the floor: no matter how catastrophically the underlying declines, the maximum loss is Rs 35,025 per lot.
Bull Put Spread Payoff Summary
Above short put strike (22,500): P&L = +Rs 2,475 per lot (max profit). Break-even (22,467): P&L = Rs 0. Between break-even and short strike (22,467-22,500): P&L between Rs 0 and +Rs 2,475 (partial profit). Between long and short strike (22,000-22,467): P&L declining loss (Rs 0 to -Rs 35,025). Below long put strike (22,000): P&L = -Rs 35,025 per lot (max loss). Break-even formula: Short put strike - net credit per unit. Maximum profit: net credit per unit x lot size. Maximum loss: (spread width - net credit) x lot size.
The Risk-Reward Asymmetry of Credit Spreads
The bull put spread's risk-reward ratio is inverted relative to debit spreads. Maximum profit = Rs 2,475. Maximum loss = Rs 35,025. Risk-reward = Rs 2,475 / Rs 35,025 = 0.07:1. For every Rs 1 of maximum profit potential, the maximum risk is Rs 14.17. This is the fundamental characteristic of credit spreads -- they offer a high probability of a small gain in exchange for a low probability of a large loss.
The probability of profit compensates for the unfavourable risk-reward ratio. If the bull put spread has a 75 percent probability of achieving maximum profit (Nifty staying above 22,500 with 3 weeks remaining), the expected value calculation: (0.75 x Rs 2,475) - (0.25 x Rs 35,025) = Rs 1,856 - Rs 8,756 = -Rs 6,900. Negative expected value -- this means the specific spread in the example (low credit yield at 7.1 percent of maximum loss) is actually a losing expected-value proposition even at 75 percent probability of success. This confirms why the minimum credit yield of 15 to 20 percent of maximum loss is critical: below that threshold, the credit spread cannot generate positive expected value regardless of how high the probability of success is.
The Low Credit-to-Loss Ratio Problem -- The Most Common Credit Spread Error
The most frequent mistake in bull put spread implementation: selecting a spread where the net credit is very low relative to the maximum loss (below 15 percent). Traders are attracted to the 'high probability' narrative of OTM credit spreads without calculating the expected value. A 90 percent probability of a Rs 2,000 gain combined with a 10 percent probability of a Rs 35,000 loss has expected value of: (0.90 x Rs 2,000) - (0.10 x Rs 35,000) = Rs 1,800 - Rs 3,500 = -Rs 1,700. Negative. The spread is mathematically expected to lose money even with 90 percent of trades being winners. Only when the credit yield is above 20 to 25 percent of maximum loss does the credit spread offer positive expected value at realistic win rates.
The Return on Margin Calculation
For credit spreads, the return on margin is the relevant performance metric -- not the absolute credit received. Return on margin = (net credit / maximum loss) x 100 = credit yield. The Rs 2,475 credit on a Rs 35,025 maximum loss (margin required) = 7.1 percent return on margin for the one-month period. Annualised: 7.1 percent x 12 = 85 percent annualised return on margin -- which sounds attractive but is deceptive because the Rs 35,025 is at risk in every losing trade. One maximum-loss outcome destroys 14.2 months of winning income. The return on margin must be evaluated in the context of the loss frequency and magnitude to assess whether the strategy is genuinely profitable over a series of trades.
Minimum acceptable return on margin (monthly): 15 to 20 percent. Below 15 percent: the credit spread does not provide sufficient income relative to the risk to be viable as an income strategy -- even small loss frequencies will produce negative total returns. Above 20 percent: the credit yield is sufficient to support positive expected value at realistic loss rates (assuming win rates above 60 to 65 percent, which require careful setup selection with OI alignment and trend confirmation).
The credit spread's apparent simplicity -- collect premium, let time pass, keep the profit -- obscures a significant risk management requirement: selecting only spreads where the credit yield is high enough to support positive expected value at realistic win rates. The low-yield credit spread that 'works 90 percent of the time' and then produces a catastrophic loss is not a profitable strategy -- it is a delayed loss machine that produces illusory gains until the inevitable large loss.
Calculate Expected Value Before Every Bull Put Spread Entry
For every bull put spread, explicitly calculate the expected value using the delta of the short put as an approximate probability estimator. Formula: EV = (probability of max profit x max profit) - (probability of max loss x max loss). The short put's delta magnitude approximates the probability of expiring ITM (probability of loss). Example: short put delta -0.20 = 20 percent probability of max loss, 80 percent probability of max profit. EV = (0.80 x Rs 2,475) - (0.20 x Rs 35,025) = Rs 1,980 - Rs 7,005 = -Rs 5,025. Negative. Do not enter. Only enter when EV is positive -- which requires both sufficient credit yield AND appropriate short put delta.