Bull Put Spreads 101: Collect Put Premium Without Going Naked
Selling a put for premium sounds steady: if the S&P 500 stays above your strike, the premium is yours. But one naked short 7400 put locks $148,000 of margin — a $10,000 paper account can't open it — and if the market falls, the loss has no floor. A bull put spread adds insurance to the naked short: sell the higher strike, buy the lower one, collect a little less premium in exchange for a capped loss and only $4,910 of margin. This page works out the math first, then shows how to practice it in the simulator.
How a bull put spread makes money
The structure is one sell and one buy: with SPX at 7550, sell one 7400 put (say, $1.50 of premium) and buy one 7350 put (say, $0.60), same expiry on both legs; the sold leg collects, the bought leg pays, for a net credit of $0.90 per share — $90.
If SPX is still above 7400 at expiry, both puts are worthless and you keep the net credit minus round-trip fees: 90 − 10 = $80 — that is the maximum profit; a bigger rally doesn't pay more.
Breakeven = short leg strike − net credit: 7400 − 0.90 = 7399.10; settle above it and you profit, below it and you start losing. Note: the simulator's spread display counts premium only; after the $10 round-trip fee ($0.10 per share), true breakeven is 7399.20.
Time is the seller's friend: a 0DTE has only today left, so both puts lose premium hour by hour — even if SPX doesn't move, the spread gets cheaper, and that decay is what the seller earns.
Why the loss is capped
The worst case is SPX settling below 7350: the short leg pays out (7400 − settlement) while the long leg pays you back (7350 − settlement); they cancel, and the loss caps at the 50-point width minus the 0.90 net credit, plus the $10 round-trip fee: a maximum loss of $4,920, no matter how far lower settlement goes.
Margin locked is only $4,910: (50 − 0.90) × 100 = 4,910; margin and maximum loss differ by just the $10 round-trip fee — don't mistake the margin locked for the maximum loss, they are two different numbers.
Compare with a naked short put: one short 7400 put locks $148,000 of margin and a $10,000 account can't open it; even if it could, a 7350 settlement costs (7400 − 7350) × 100 − 150 + 1.30 = $4,851.30, and the loss keeps growing as settlement falls — no cap.
A 1% SPX move is about 75 points on a 0DTE day, wider than the 50-point spread — a spread caps the loss, it doesn't prevent hitting the cap; don't size the trade for a calm day.
How to practice in the simulator
First, the plain truth: you can't open a naked short put in the simulator — selling locks 20% of the strike as margin, so a 7400 put locks $148,000 while the starting virtual balance is only $10,000, and submitting reports "insufficient margin". Use a bull put spread instead: sell the 7400 put and buy the 7350 put — a live test opens 1 contract locking $4,910 of margin, collecting $90 of premium net, with a $5 opening fee, a maximum profit of $80 and a maximum loss of $4,920.
How to practice: pick a pair of puts on the chain, work out the breakeven first (net: short leg strike − net credit + per-share fee: 7400 − 0.90 + 0.10 = 7399.20), write your exit plan before you submit; no new opens after 3:30 p.m. ET, and sort out positions before the 3:55 p.m. reminder — don't leave it to the close.
Spread fees: a vertical spread is charged $2.50 per leg per side — $5 to open one spread, $5 to close it, $10 round trip; one spread open counts as 1 open against the daily limit, not per leg.
Practice it side by side with the naked short: the naked put's breakeven is 7398.51 (7400 − 1.50 + 0.013), the spread's is 7399.20 — the spread gives up 0.69 points to cap the loss and open with $4,910; decide whether that trade is worth it before you pick which one to practice.
Four mistakes beginners make
Mistaking the $4,910 margin locked for the maximum loss: the maximum loss is $4,920 — the $10 gap is the round-trip fee. Margin is the money you post to open; maximum loss is the worst expiry outcome. Don't mix them up.
Looking at the $90 net credit but not at how far the strike is from spot: 7400 sits 150 points below spot at 7550, and a 1% SPX day is 75 points — two such days reach breakeven. Ask "how far down before I lose" before "how much do I collect".
The wider the spread, the more you collect — and the more you can lose: a 50-point-wide spread can lose up to $4,920; a 10-point-wide one (say, sell 7400, buy 7390) can lose at most (10 − net credit) × 100 + $10. Decide the most you can lose first, then work backwards to how wide the spread can be.
Opening with no exit plan: a 1% SPX move is 75 points on a 0DTE day, and premium can double in a moment — decide how much you'll lose and by when before you open, not at the close.
This simulator uses real CBOE option chains delayed about 15 minutes, starts with $10,000 in virtual funds, charges $0.65 per contract per side in fees, and shows P&L net of fees; short-sale margin is a simplified simulated rule at 20% of the strike, not a real broker margin. The simulator is for practicing orders, discipline, and review. It is not investment advice and promises no returns.