Bull Put Spreads: Capital Efficiency, Win Rates, and Spread Width Math

A Bull Put Spread (credit put spread) gives you roughly 19× the capital efficiency of a Cash-Secured Put while capping your downside at a known dollar amount before you enter. You sell a put at a higher strike, buy a protective put at a lower strike — same expiration, same stock — and pocket the difference in premiums.

💡 See the capital gap yourself: Open the live CSP calculator — at $25K account on a $170 strike, one CSP eats 68% of your portfolio. A $5-wide BPS on the same strike commits roughly $500.

The Math in One Example

Stock XYZ trades at $100. You sell the $95 put for $2.00 and buy the $90 put for $0.50, collecting a $1.50 net credit ($150 per contract).

• Max profit: $150 — if XYZ stays above $95 at expiration
• Max loss: $350 — if XYZ drops below $90 (spread width $5.00 minus credit $1.50, times 100)
• Breakeven: $93.50 — the stock can fall 6.5% before you lose a dollar
• Return on capital: 42.9%

Compare that to a cash-secured put at the $95 strike: same directional bet, but you'd tie up $9,500 in collateral. The spread uses $350–$500 depending on your broker. That freed-up capital lets you diversify across many positions instead of concentrating in one.

How Spread Width Changes Everything

Width is not just a detail — it fundamentally reshapes the risk profile. Using a $100 stock with a $95 short strike:

• $2-wide (95/93): $0.65 credit, 48.1% ROC, 2.08:1 risk-reward
• $5-wide (95/90): $1.50 credit, 42.9% ROC, 2.33:1 risk-reward
• $10-wide (95/85): $2.50 credit, 33.3% ROC, 3.00:1 risk-reward

Narrower spreads produce higher percentage returns — tempting traders to stack multiple contracts. Here's the trap: five $2-wide contracts deploy similar capital to one $10-wide spread, but create 5× the exposure at the short strike. When the stock crashes through, those equivalent-capital narrow spreads lost more than double what a single wide spread lost in backtests. The $5-wide spread is the consensus sweet spot.

A practical filter: target a net credit of at least one-third the spread width. For a $5-wide spread, that means collecting at least $1.65. This keeps your breakeven win rate below the probability of profit you're actually selling.

Win Rates: What the Data Shows

At 1 standard deviation (~16 delta), the theoretical probability of the short put expiring worthless is about 84%. In practice, it's better. Option Alpha's five-year SPY backtest showed a 93% win rate held to expiration. ProjectFinance's study of 41,600 trades on SPY (2007–2017) confirmed that managing 16-delta short puts at 50% of max profit pushes effective win rates to 88–90% while significantly reducing maximum drawdown.

At 2 standard deviations (~5 delta), win rates exceed 95%, but the premium is razor-thin. Spintwig's backtesting found 5-delta SPX put spreads generated only about $1,500 over a multi-year period — the credits are too small to build meaningful income, and a single loss erases months of gains.

The structural edge behind these numbers is the volatility risk premium: implied volatility overstates realized volatility roughly 85% of the time, with an average spread of 2–4 percentage points on SPY. Over the 2007–2026 window, the CBOE PutWrite Index — selling ATM S&P 500 puts — delivered 7.0% annualized with only 10.9% volatility vs. the S&P 500's 15.4% (the longer 1986–2018 window produced 9.54% annualized; different sampling periods explain the gap).

Margin: Where Your Broker Matters

The standard margin formula is identical everywhere: spread width × 100. For a $95/$90 spread, that's $500. Where brokers differ is whether they subtract the credit received:

• Interactive Brokers: Full width held — $500 buying power effect
• Schwab: Credit applied in practice — ~$350–$400
• Tastytrade: Credit explicitly subtracted — ~$350

Schwab requires Level 2 options approval and a margin account for spreads. IRA spread trading requires a $5,000 minimum at Schwab. Tastytrade has the most favorable treatment with no account minimum beyond $2,000 for margin privileges.

The Greeks Work in Your Favor — Until They Don't

When the spread is out-of-the-money, theta is positive (time decay earns you money daily), vega is negative (declining volatility helps), and gamma is near zero (your position stays stable). These favorable dynamics flip if the stock crashes through the short strike — then gamma spikes, delta moves against you fast, and the long put becomes your lifeline.

Managing winners at 50% of max profit avoids this danger zone. Tastytrade's research consistently shows this produces equivalent annualized returns to holding through expiration but with dramatically lower drawdowns. The freed-up capital gets redeployed into new trades.

Small Accounts: Why Spreads Are the Only Real Option

A $5,000 account can sell exactly one cash-secured put on a $50 stock — a single concentrated bet. That same $5,000 in $5-wide spreads at ~$450 buying power each supports 10–11 simultaneous positions across different stocks and sectors. Option Alpha advises accounts under $25,000 to focus exclusively on defined-risk strategies: credit spreads, iron condors, iron butterflies. No naked risk.

The danger is overleveraging. Because each spread requires so little capital, traders can easily open 20+ positions and find themselves fully exposed during a correlated selloff. Best practice: keep 50–60% of capital active at most. A single $5-wide spread losing its max $350 is survivable. Twenty of them losing simultaneously is not.

CSP vs. BPS: Capital Profile Comparison

• CSPs suit accounts of $50,000+, traders who genuinely want to own the stock, Wheel strategies, or stocks with meaningful dividends
• BPS suit capital-limited accounts, defined-risk preferences, multi-position diversification, or IRAs with limited funds
• Both can coexist in accounts above $25,000 — CSPs on conviction stocks, BPS on everything else

ThetaLoop's X-Ray scores apply to the underlying stock. Regime, momentum, and volatility matter whether you sell a naked put or a spread — the scoring doesn't change, only your capital structure does.

The Bottom Line

Bull put spreads trade a capped, asymmetric payoff for high probability and extreme capital efficiency. The volatility risk premium — confirmed by decades of CBOE data — provides a structural tailwind. The 1-SD sweet spot (~16 delta) balances meaningful premium against high win rates, and managing at 50% transforms the risk profile from lumpy to smooth. For accounts under $25,000, spreads aren't just recommended — they're practically the only viable path to diversified options income.