How Much to Risk Per Options Trade: Position Sizing Basics

Most options sellers spend careful time choosing the right strike, the right expiry, and the right underlying. They spend almost no time deciding how large the position should be. That imbalance is a mistake. A bad position sizing decision can turn a string of winning trades into a net-losing year — or worse, a margin call that forces you out of positions at the worst possible time.

This guide covers the basics of sizing a cash-secured put or covered call position within a real portfolio.

What problem does position sizing solve?#

You sell options to collect premium. Over many trades, the probabilities work in your favour — most options expire worthless, and sellers capture that statistical edge. But “over many trades” is the key phrase. A single oversized position, hit by a sharp, fast decline, can erase months of small gains in a week.

Position sizing is the discipline that keeps any single loss bounded. It answers the question: what is the most I should put at risk on any one trade, given my total portfolio size?

The percentage-of-portfolio framework#

The simplest and most widely used approach is to cap each position at a fixed percentage of total portfolio value. For options sellers running cash-secured puts, a common rule is to commit no more than 5–10% of total portfolio capital to any single underlying.

If your trading account holds $100,000 and you apply a 5% limit, you should not have more than $5,000 reserved in cash for any one cash-secured put. For a $50 stock, one contract ($50 × 100 = $5,000) sits at that limit. For a $100 stock, one contract ($10,000) already exceeds it — you would need a portfolio of at least $100,000 to run one $100-stock CSP at the 10% limit.

This is why stock price matters in practice, not just in theory. You cannot easily sell a cash-secured put on a $500 stock in a $50,000 account without violating reasonable position sizing. You either need a larger account, a lower-priced underlying, or a spread-based strategy.

Do correlated options positions count as diversification?#

Five cash-secured puts on five different stocks might look diversified. But if all five are technology stocks, they are not — in a broad selloff or a sector rotation out of tech, all five will likely fall together. Your five positions behave like one larger position.

Genuine diversification for an options seller means spreading across underlyings that respond differently to the same macro events. A mix of a large-cap tech stock, an industrial, a consumer staple ETF, and a financial will not move in lockstep the way a pure-tech basket would.

The practical implication: count correlated positions as partial duplicates when you assess concentration. Two large-cap tech CSPs are not two independent risks — they are closer to one and a half. Adjust your sizing accordingly.

The Kelly Criterion: a mathematical framework#

The Kelly Criterion is a formula for sizing positions based on the probability and payoff of each trade. Properly applied, it theoretically maximises the long-term growth rate of a portfolio. The formula:

Kelly fraction = (p × b − q) / b

Where p is the probability the trade wins, q is the probability it loses (1 − p), and b is the ratio of gain to loss.

For a typical cash-secured put: say you sell a put with a 70% probability of expiring worthless. Your premium is $2.00 and your maximum loss (if the stock goes to zero) is the strike price minus the premium — but realistic losses on quality stocks in normal markets are far smaller. If you model a realistic worst-case loss of $8.00 (the stock falls $10, you lose $10 per share minus the $2 premium), the Kelly formula suggests allocating roughly 15–25% of capital to the trade.

That number surprises many people — it is often higher than they expected. The reality is that Kelly gives you a theoretical maximum for long-run growth, not a practical recommendation. Most practitioners use half-Kelly (allocating half the Kelly-suggested amount), which dramatically reduces volatility of outcomes while sacrificing only a small amount of long-run growth. Half-Kelly on a 70% win-rate trade with a 4:1 loss-to-win ratio might suggest 7–12% of portfolio per position.

The important thing about Kelly is not the exact number — it is the variables it forces you to think about: your actual win rate, your actual gain-to-loss ratio, and how those compound across many trades.

CSP-specific sizing considerations#

A cash-secured put has a fixed capital requirement: strike × 100 shares per contract. This gives you less flexibility than a stock position. You cannot own half a contract. The sizing decision becomes: how many contracts, and at what strikes, to stay within your percentage limit?

For a $100,000 account with a 5% per-position limit ($5,000 maximum):

• A $45 stock: one contract = $4,500 — fits within the limit.
• A $50 stock: one contract = $5,000 — right at the limit.
• A $80 stock: one contract = $8,000 — exceeds the 5% limit; you would need to use the 8% limit or move to a lower strike.
• A $150 stock: one contract = $15,000 — too large for a 5–10% limit in a $100,000 account. Choose a different underlying or wait until your account is larger.

This is the practical constraint that makes ETFs like SPY attractive to smaller accounts — the lower per-share price (relative to many quality stocks) makes contract sizing more manageable. The tradeoff is lower premium per dollar of capital because ETF IV is typically lower than individual stocks.

Running multiple positions simultaneously#

Sizing each position correctly is necessary but not sufficient. You also need to think about the total capital deployed across all open positions at once.

If you have five open cash-secured puts each at 7% of your portfolio, you have reserved 35% of your portfolio as cash collateral. That is healthy — you still have 65% available as a buffer. If you run ten positions at 7% each, you have 70% deployed, with only 30% free. That is workable but starting to concentrate. Beyond that, you are approaching a situation where a broad market decline tests every position simultaneously, and you have limited remaining capital to add positions at better prices.

A common framework among systematic options sellers: deploy no more than 40–60% of total portfolio capital in options collateral at any one time, leaving the remainder as a cash buffer and opportunity reserve.

What is the risk of ruin in trading?#

The deepest position-sizing argument is not about maximizing return — it is about avoiding ruin. Ruin in this context does not mean losing everything, but losing enough that you cannot meaningfully continue trading.

A 20% drawdown from oversizing a handful of trades is recoverable. A 50% drawdown is psychologically devastating and mathematically requires a 100% gain just to return to the starting point. Position sizing is the primary lever that controls how large any drawdown can be before the market gives you a chance to recover.

Use the position sizing and Kelly simulator tools below to model your own account. Input your typical premium, your estimated win rate, and your loss assumptions — then see how the Kelly and half-Kelly recommendations compare to what you have been doing. The gap between the two often reveals where the real sizing risk lives.