Trading Calculators

Position Sizing Calculator

Calculate the right number of shares to buy for this trade from your acceptable loss relative to your account and your stop-loss price.

Calculated in your browser only · inputs are not saved

Enter your values and press Calculate

Right-sized quantity to buy

Amount invested

Share of account

Reward-to-risk ratio

Risk management

How much to buy is decided by how much you can afford to lose

If you size your trade so that you lose only 1 to 2% of your account when the stop-loss price is hit, you can protect your account even through a losing streak.

Set your acceptable loss
Decide your total account value and the percentage loss you are willing to take on a single trade.
Entry price and stop-loss price
Set the stop-loss price first, for example at a chart support level, then enter your entry price.
Check the quantity
Quantity is set by acceptable loss ÷ loss per share. If it exceeds the weight cap, it is reduced automatically.

Shares to buy = (total account value × acceptable loss rate) / (entry price − stop-loss price)

The reward-to-risk ratio (R) is (target price − entry price) / (entry price − stop-loss price). With a ratio of 2 or higher, the expected value can still be positive even with a 40% win rate.

FAQ

What happens if I set a wide stop-loss?

Loss per share gets larger, so the quantity you can buy for the same acceptable loss shrinks. Stop-loss distance and quantity are inversely proportional.

Can I use it for short selling or bets on a decline?

If the stop-loss price is entered higher than the entry price, it is treated as a short position and calculated the same way.

Why do I need a weight cap?

If the stop-loss distance is very narrow, the calculated quantity can become excessively large. To prepare for situations where a stop-loss cannot be filled, such as a gap down, it is safer to also set a maximum weight per stock.

Results are estimates based on your inputs and simplified assumptions, and are for reference only, not a basis for investment decisions.