Position size calculator
“Given my account size, the share of it I am prepared to lose on this trade, and where my stop is — how many shares, contracts or lots is that?”
Every trade needs a quantity, and the quantity is the only input that decides what a stop-out costs. This calculator turns an account size, a risk percentage and the distance from entry to stop into a unit count — on any instrument, because an instrument's behaviour is captured by one number: its point value.
Free to use, nothing to sign up for, and nothing you type here is sent anywhere — the arithmetic runs in your browser.
What it computes
risk budget = account x risk% per-unit risk = |entry - stop| x point value units = FLOOR(risk budget / per-unit risk) actual risk = units x per-unit risk notional = units x entry x point value leverage = notional / account
What you type in
| Field | What it means | Example |
|---|---|---|
| Account size | The capital the risk percentage is taken from. | $25,000 |
| Risk per trade % | The share of the account a stop-out would cost. | 1% |
| Entry price | The planned entry. | 100 |
| Stop price | The exit-for-a-loss price. Its distance from entry sets the per-unit risk. | 98 |
| Instrument | A preset supplying the point value: stock/ETF = 1, a futures contract = its multiplier, forex = the per-unit value, or custom. | Stock / ETF |
Reading the result
- Units — the headline: shares, contracts or lots.
- Actual risk — what a stop-out costs at that size. It can read slightly under the budget, because the remainder does not buy a whole unit.
- Notional — the position's face value. Leverage is that divided by the account.
- “Too small” — shown when even one unit exceeds the budget. Not an error: the stop is too wide, or the risk share too small, to fund a single unit of this instrument.
- A risk-level table repeating the same arithmetic at several percentages, so the size's sensitivity to that one input is visible.
Worked example
$25,000 account, 1% risk, entry 100, stop 98, stock.
- Risk budget = 25,000 x 1% = $250
- Per-unit risk = |100 - 98| x 1 = $2
- Units = floor(250 / 2) = 125 shares
- Actual risk = 125 x 2 = $250
- Notional = $12,500, leverage 0.5x
Change nothing but the instrument and the answer inverts: an ES futures entry at 5000 with the stop at 4990 is 10 points at a $50 point value, so one contract risks $500 — more than the whole $250 budget. The tool returns zero units and says too small. That is the honest answer, and it is why the point value field exists.
What trips people up
- The point value is the whole game on non-equities. Leave it at 1 for a futures contract and the result is 50x too large.
- Entry and stop are prices, not distances. The absolute difference is used, so long and short both work without a direction switch.
- Rounding is always down, so the realised risk lands at or below the budget, never above it.
- Zero units is a real answer, not a bug.
- The result is the maximum size the risk budget funds. It takes no view on anything else about the trade.
Questions
- What risk percentage does it use?
- Whichever you type. The field defaults to 1% because it is a common convention in trading literature, and the risk-level table shows several others side by side. The calculator does not recommend one.
- Does it work for futures and forex?
- Yes. Pick the instrument preset, or type a custom point value. A futures contract's multiplier and a forex lot's per-unit value go in the same field, and the arithmetic is identical from there.
- Why is my answer zero?
- One unit of that instrument would risk more than the budget allows — usually a wide stop, a small account, or a large point value. Narrowing the stop, raising the risk share or choosing a smaller contract are the three things that change it.
Related calculators
These are the same calculators built into Ledger of Alpha, where they read your own trade history instead of numbers you re-type. See the full product
Keep the record these numbers come from
A free account logs the trades you size here, so the win rate and averages you type into these calculators come from your own history rather than a guess.