How to calculate position size
Position sizing answers the single most important question in trading: how many shares or units should you actually buy? The answer comes from how much you are willing to lose, not how much you hope to make. First decide the dollars you will risk — your account size times your risk percentage — then divide that budget by the risk on a single share, which is the distance between your entry and your stop-loss:
Shares = (Account × Risk%) ÷ |Entry − Stop|
The stop distance is taken as an absolute value, so it works the same whether you are long or short — there is no direction to set. For futures, multiply the per-unit risk by the contract multiplier so dollar risk and position value are correct.
Worked example
You have a $10,000 account and risk 1% per
trade, so your risk budget is $100.
You plan to enter at $100 with a stop at $95,
so the risk per share is $100 − $95 = $5.
Shares = $100 ÷ $5 = 20 shares.
Position value = 20 × $100 = $2,000, and if the stop is hit
you lose only your planned $100.
Why risk-based sizing matters
Most traders pick a round number of shares and hope for the best, which means every trade risks a different — and unknown — amount of capital. Sizing each position to a fixed percentage of your account flips that around: your loss on any single trade is capped before you enter, so a losing streak draws your account down slowly instead of blowing it up. It also removes emotion from the decision, because the number of shares is simply math, not a gut feeling about how confident you are.
How much should you risk per trade?
The risk percentage you choose decides how many losing trades in a row your account can absorb. The table below shows your remaining capital after ten straight losers at each risk level — a useful sanity check before you nudge the percentage up:
| Risk per trade | $ risked on a $10,000 account | Account left after 10 losses |
|---|---|---|
| 0.5% | $50 | ≈ $9,511 (−4.9%) |
| 1% | $100 | ≈ $9,044 (−9.6%) |
| 2% | $200 | ≈ $8,171 (−18.3%) |
| 3% | $300 | ≈ $7,374 (−26.3%) |
Each figure compounds the loss (0.9910, 0.9810 and so on), which is why drawdowns grow faster than the headline percentage suggests. Most professionals stay between 0.5% and 2%. Once you know your share count, the stop loss / take profit calculator sets your exact exit prices, and the risk/reward calculator tells you the win rate that position size needs to be profitable.
Position size vs the stop distance
Notice that a tighter stop produces a larger share count for the same dollar risk: halving the distance between entry and stop doubles the number of shares that fit inside your risk budget. That is the lever most traders miss — your break-even price and your stop placement do more to set position size than your account balance does. If you average into a position, recompute against your blended entry from the average down calculator before sizing the next add.
Frequently asked questions
- How do you calculate position size?
- First find the dollars you are willing to risk: account size × risk %. Then divide that by your per-unit risk, which is the absolute distance between your entry and stop-loss price. Shares = (account × risk%) ÷ |entry − stop|. The result is the largest position that keeps your loss within your risk limit if the stop is hit.
- What risk per trade should I use?
- Most professional traders risk between 0.5% and 2% of their account on any single trade. Risking 1% means a string of ten losing trades only draws your account down about 10%, leaving plenty of capital to recover. The quick-fill chips give you 0.5%, 1%, 2% and 3% in one tap.
- Why is position sizing more important than entry price?
- Your entry decides whether a trade wins or loses, but your position size decides how much it costs you when you are wrong. Sizing every trade to a fixed percentage of risk keeps any single loss survivable and removes emotion from how many shares to buy.
- Can I use it for crypto and futures?
- Yes. Crypto supports fractional quantities and small decimal prices. For futures, set the contract multiplier (for example 50 for the E-mini S&P 500) so the per-unit risk and position value are correct. Forex is coming soon.
- What if the calculated position is larger than my account?
- It can happen when your stop is very tight: a small per-share risk divides into your risk budget many times, producing a position value above your cash. The calculator still shows the risk-correct quantity, but check the "Position value" row — if it exceeds your buying power you either need a wider stop, a smaller risk percentage, or to accept a smaller (capped) position.
- Why does it show a whole-share quantity and an "actual risk"?
- Stocks usually trade in whole shares, so the raw quantity is floored to the nearest whole number. Rounding down slightly reduces your real exposure, so the "Actual risk" row recomputes the dollars at risk for that whole quantity (plus fees) — the true amount you stand to lose if the stop is hit.