How to size a trade with this calculator
Enter four things — your account size, how much you’re willing to risk on the trade (as a percentage of the account or a fixed dollar amount), your intended entry price, and your stop-loss price. The calculator returns the exact number of shares or contracts that risks precisely your chosen amount if the stop is hit, along with the position’s dollar value and its share of your account.
The formula
Risk-based position sizing is a two-step calculation. First, work out how many dollars you’re
risking: risk amount = account size × risk % (or your fixed dollar figure). Then
divide that by the risk per share, which is the distance from entry to stop:
shares = risk amount ÷ |entry − stop|. For futures, the price distance is converted
to dollars per contract through the instrument’s tick size and tick value before dividing.
Because partial shares and contracts aren’t tradable, the result is always rounded down. That’s deliberate: rounding up would push your risk past the limit you set, which is the one thing a risk tool should never do. The calculator then shows the true dollars at risk after rounding.
A worked example
Say you have a $25,000 account and risk 1% per trade — that’s $250. You want to buy a stock at $190 with a stop at $186, so your per-share risk is $4. Dividing $250 by $4 gives 62.5, which rounds down to 62 shares. Those 62 shares put $248 at risk (just under your $250 target) and represent an $11,780 position — about 47% of the account.
Position sizing for futures
Switch the calculator to Futures and pick your contract. Each contract carries a tick size and a dollar value per tick — for the E-mini S&P 500 (ES), a tick is 0.25 index points worth $12.50. If your entry-to-stop distance is 5 points, that’s 20 ticks, or $250 of risk per contract. A $500 risk budget therefore sizes to 2 contracts. TradeCaliper stores the tick specs for common index, energy, and metals contracts so you don’t have to look them up.
Common mistakes this prevents
- Sizing off gut feel instead of a fixed, repeatable rule.
- Using a forex-style lot calculator that doesn’t model stock or futures risk correctly.
- Rounding share counts up and quietly taking on more risk than intended.
- Ignoring how large a position is relative to the account (leverage creep).
TradeCaliper is a planning and education tool, not financial advice.