Understand a Bull Put Spread Strategy

This guide explains how a bull put spread works on Nifty, the numbers on one lot, how to choose strikes, how it behaves before expiry, how to manage it and how to automate and test it.

At a glance

How a bull put spread works

Selling a put on its own earns premium if the index stays up, but a sharp fall can bring a large loss, and the margin is high. Buying a lower put turns it into a defined-risk trade:

• The bought put limits the loss to the gap between the strikes, minus the credit.
• The credit is smaller than for the put alone, because part of it pays for the protection.
• The hedge lowers the margin the broker blocks.

The spread profits if the index rises, stays flat or falls only a little. It loses only if the index falls below the breakeven.

The numbers on one lot

Using Black–Scholes model prices with Nifty at 25,000, 12 days to expiry, IV of 14% and a lot of 65:

• Sell the 24,800 put at ₹145.35
• Buy the 24,500 put at ₹65.35
• Net credit: ₹80.00 per unit, or ₹5,200 per lot

The strikes are 300 points apart. The maximum loss is 300 minus the 80 credit, or 220 per unit, ₹14,300 per lot. You risk about ₹2.75 for every ₹1 of credit.

In the model, the chance that Nifty finishes above the 24,800 short strike, for the full credit, is about 65%. The chance that it finishes above the 24,720 breakeven is about 70%. A high win rate with a small reward is the trade-off of every credit spread: one maximum loss erases almost three full wins.

Choosing strikes

The short strike

The short strike is the level you expect the index to hold. Selling closer to the money collects more credit but wins less often. Here is the trade with three short strikes, each hedged 300 points lower:

Many traders sell a put with a delta between −0.25 and −0.35. The 24,800 put has a delta of about −0.34.

Width of the spread

A wider spread collects more credit but has a larger maximum loss. A narrow spread risks less per lot, but brokerage and taxes take a bigger share of a small credit. Choose the width from the loss you can accept on one lot, then set the number of lots.

How a bull put spread behaves before expiry

At entry the spread has a delta of about +0.15 per unit, so a 100-point rise in Nifty adds about ₹1,000 per lot at first. Its theta is about +₹124 a day per lot: time decay works for you while Nifty is above the short strike. Its vega is about −₹290 per lot for each 1-point rise in IV, so a jump in volatility hurts even if Nifty does not move.

With 6 of the 12 days left, the model shows:

Most of the credit is earned in the last days, as with any short option. If Nifty falls to the short strike early, the loss on screen is still well below the maximum, which leaves room to exit.

When a bull put spread works, and when it does not

Works best when:

• Nifty is in an uptrend or holding above a clear support level.
• IV is high and likely to fall, such as after a result or policy event.
• You can name a level the index is unlikely to break before expiry.

Struggles when:

• The index falls sharply, especially with a gap at the open that skips your stop.
• Volatility rises, which raises the value of the put you sold.
• You sell too close to the money to collect a bigger credit.

Managing a bull put spread

• Take profits early. Many traders buy back the spread once it has earned 50% to 70% of the credit.
• Set a loss limit. A common rule is to exit if the spread's value doubles, a loss of about one credit.
• Exit on a break of support. If Nifty closes below the level the trade relied on, the view is wrong.
• Plan for expiry day. An extra 2% exposure margin applies to short index options on expiry day, and the spread's value swings fast near the short strike.
• Roll down if the view still holds. Close the spread and open a new one at lower strikes, with time left to recover.

Bull put spread vs other bullish strategies

With the same strikes, a bull put spread and a bull call spread have almost the same payoff at expiry. The choice comes down to margin, liquidity and whether you prefer to collect premium or pay it.

Automating a bull put spread

In QuantPower's strategy builder, the spread is two legs with a shared entry rule:

1. Set the entry condition, such as a time, Nifty above a moving average, or a hold above support.
2. Buy the 24,500 put first, then sell the 24,800 put, so the broker sees a hedged position for margin.
3. Set a target at 60% of the credit and a stop when the spread's value doubles.
4. Add a time exit before the close on expiry day.

An MTM stop loss across all positions adds a second safety net. Test the rules in paper trading before going live.

Backtesting a bull put spread

Useful variables to test:

• the entry filter, such as trend direction or day of the week,
• the short strike's delta, from −0.20 to −0.40,
• the width, 200 to 500 points,
• the target and stop, and
• the days to expiry at entry.

Judge the results by the average profit per trade after costs and by the worst loss, not by the win rate. Credit spreads win often and lose more when they lose. Our guide to backtest performance metrics explains what to look at.

Common bull put spread mistakes

• Selling too close to the money. The extra credit rarely pays for the lower win rate.
• Holding to the maximum loss. Without a stop, one bad week undoes many good ones.
• Legging in. Selling the put first and buying the hedge later leaves you exposed, and the margin is higher.
• Selling cheap premium before an event. If IV is low and a result or policy decision is due, the credit does not pay for the risk.
• Sizing up because of the win rate. Size by the maximum loss, not by how often the trade wins.

Frequently asked questions

Sources

• Black, F. and Scholes, M. (1973). The Pricing of Options and Corporate Liabilities. Journal of Political Economy, 81(3), 637–654
• NSE: Equity derivatives contract specifications
• SEBI circular SEBI/HO/MRD/TPD-1/P/CIR/2024/132: Measures to strengthen the equity index derivatives framework, 1 Oct 2024