Position Sizing When Your Stop Is on the Option, Not SPY
Sizing a stock trade is easy: risk divided by stop distance. Options add the 100 multiplier and a stop that lives on the premium, and getting the math right is the difference between controlled risk and a blowup.
On an options scalp, your stop is on the option's premium, and every contract controls 100 shares' worth of movement. So position sizing means working backward from the dollars you're willing to lose to the number of contracts — never forward from “how many can I afford.”
The formula
Your dollar risk per contract is the premium distance to your stop, times 100: risk per contract = (entry premium − stop premium) × 100.
Then: contracts = (dollars you'll risk) ÷ (risk per contract). Example: you'll risk $200, you buy at $1.30 with a stop at $0.90 → risk per contract = (1.30 − 0.90) × 100 = $40 → you can trade 5 contracts (5 × $40 = $200). The stop distance and your risk budget set the size; you don't guess.
Why you work backward
The wrong way — “I have $2,000 buying power, I'll buy $2,000 of options” — ignores the stop entirely and takes wildly variable risk. Working backward from a fixed dollar risk (your 1% or so) keeps every trade's risk constant regardless of the option's price, which is the whole point of position sizing (see fixed-dollar vs fixed-contract).
Size isn't “how many can I buy?” It's “how many keep my loss at my number if the stop hits?” Solve backward, every time.
The 0DTE reality
Because a 0DTE option is heavily leveraged and can move fast, small premium moves are big dollar moves, so this math matters more, not less. Note also that a same-day option can gap or the spread can widen, so the realized loss can exceed the intended stop (build in a cushion — see why a dollar stop beats a percent stop). The free position-size calculator does this backward-from-risk math for you — dollar risk in, contract count out.
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NoVo is a software tool for market analysis, not financial advice. This article is general education, not investment advice. Options trading involves substantial risk of loss, up to and including your entire capital. NoVo makes no guarantee of profit, win rate, or performance, and past results do not predict future outcomes. You are responsible for your own broker account, configuration, and trading decisions.
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