The position size formula#
Position sizing answers one question: how big can this trade be so that, if it hits my exit, it costs exactly the amount I planned? The formula is the same in every market:
- Risk in dollars = risk budget × risk per trade (%).
- Position size = risk in dollars ÷ stop distance (%).
The part most calculators get wrong for a funded account is the first input. Your risk budget is not your balance. It is the distance from your balance to the drawdown floor, because that is the room you trade within. On a fresh $25,000 Fullport account the floor is $24,000, so the budget is $1,000 — 4% of what the dashboard shows. Once a day closes at $26,000 or more the floor locks at $25,000, and from then on the budget is simply balance − $25,000.
| Risk per trade (of the $1,000 budget) | Risk in dollars | Position at a 30% stop | Full-stop trades the budget covers |
|---|---|---|---|
| 5% | $50 | $167 | 20 |
| 10% | $100 | $333 | 10 |
| 25% | $250 | $833 | 4 |
| 50% | $500 | $1,667 | 2 |
Swipe or scroll to compare all columns.
Stop distance on memecoins, with costs included#
Memecoin stops are wide because the coins are. A 30% move against you on a curve-stage coin is an ordinary candle, so a 5% stop tends to exit on noise. Set the stop where the trade idea is wrong, then let the formula shrink the size to fit.
Then add costs to the stop, because they come out of the same budget. On the pump.fun curve each side pays the venue's swap fee (about 1.25%) plus Fullport's 1% platform fee, so a round trip costs about 4.5% before price impact and network fees (fill policy). A trade with a 30% stop really risks about 34.5% of the position. With $100 at risk, that is a $290 position instead of $333.
The floor is compared with live equity: cash plus the marked value of everything you hold, on every tick. Three positions that each put $300 at stake use $900 of a $1,000 budget together, so size each new trade against the budget left after the others.
Liquidity: the 15% impact cap#
The second limit has nothing to do with your risk tolerance. Before any Fullport order fills, the engine quotes it against a fresh read of the coin's curve or pool. If your average fill price would be more than 15% worse than the spot price before the order, it is rejected with IMPACT_CAP instead of being filled (rules). Inside the cap, the impact is charged to you as part of the fill.
On a constant-product pool a buy of x dollars into a quote-side reserve Q moves your average price by roughly x ÷ Q. Q is about half of the liquidity figure most charts show, because that figure counts both sides of the pool. So the largest buy under the cap is about 15% of Q, or 7.5% of the quoted liquidity:
| Quoted pool liquidity | Quote reserve (Q) | Largest buy under 15% | Impact of a $1,000 buy |
|---|---|---|---|
| $20,000 | $10,000 | $1,500 | 10% |
| $50,000 | $25,000 | $3,750 | 4% |
| $200,000 | $100,000 | $15,000 | 1% |
Swipe or scroll to compare all columns.
On small accounts risk is usually the binding limit. On large ones, liquidity takes over. A $125,000 account has a $5,000 budget; risking 10% of it at a 30% stop is a $1,667 position, which would cost about 16.7% impact in a $20,000 pool and be rejected. The calculator flags that case in red. Split the order, pick a deeper pool, or accept a smaller position.
Using the numbers#
Re-run the sizing whenever the budget changes: after each trading day, after the floor ratchets, and after it locks. The drawdown calculator gives you the floor for any sequence of closes. To see what a single order does to a pump.fun curve, including how many tokens you receive and how far it moves the price, use the bonding curve calculator. Orders themselves are placed in the browser terminal or through Fullport Tap.
Quick answers
- How do you calculate position size in crypto?
- Decide the dollar amount you are willing to risk if the trade hits your exit, then divide it by the stop distance as a percent. Risking $100 with a 30% stop gives a $333 position. On a funded account, base the dollar risk on the distance to your drawdown floor, not your balance.
- How much should I risk per trade on a funded account?
- Express it as a share of the room above your floor, not of the balance. On a fresh $25,000 Fullport account that room is $1,000, so risking 10% of it ($100) gives you room for ten full-stop trades, while risking 1% of the balance ($250) gives you room for four.
- Why was my memecoin order rejected for size?
- If the order would make your average fill more than 15% worse than the spot price, Fullport rejects it with IMPACT_CAP rather than filling it at an unrealistic price. Split the order, choose a deeper pool, or reduce the size. Impact inside the cap is charged on the fill.
- Do fees count toward my position size risk?
- Yes. Fees are paid from the same balance the floor protects. On the pump.fun curve the venue fee is about 1.25% per side and Fullport's platform fee is 1% per side, so add about 4.5% to your stop distance before sizing, plus impact and network fees.