Compounding means the bot reinvests profits, so position sizes grow as the account grows. Fixed sizing means it trades the same amount forever. Compounding earns more when things go well — that's the famous snowball — but it also makes drawdowns bigger in dollar terms. The honest answer: compound, but on a schedule, not on every trade.
What's the difference between compounding and fixed position size?
Fixed sizing bets the same dollar amount every time; compounding recalculates the bet from the current account balance. Say a bot starts with $1,000 and risks its full balance each period. Under fixed sizing, it always trades $1,000 worth, and any profit sits to the side. Under compounding, after a winning period the balance might be $1,020, so the next trade is sized on $1,020 — the profit goes back to work. The difference sounds cosmetic. It isn't: fixed sizing grows your account in a straight line (same average dollars added each period), while compounding grows it in a curve that steepens over time, because every gain enlarges the base that the next gain is calculated on.
How much extra does compounding actually earn?
Modestly more at first, then increasingly more the longer it runs — here's the math from stated assumptions. Assume a bot reliably makes 2% per period on whatever it trades (an assumption for arithmetic's sake, not a promise — no real bot is this steady). Start with $1,000. Fixed sizing earns 2% of $1,000 = $20 every period: after 12 periods, $1,000 + 12 × $20 = $1,240. Compounding multiplies the balance by 1.02 twelve times: $1,000 × 1.02¹² = $1,268.24.
| After period | Fixed sizing | Compounding |
|---|---|---|
| 4 | $1,080.00 | $1,082.43 |
| 8 | $1,160.00 | $1,171.66 |
| 12 | $1,240.00 | $1,268.24 |
| 36 | $1,720.00 | $2,039.89 |
Twelve periods in, compounding is ahead by only $28. But stretch to 36 periods and the gap is $320 — the curve pulls away from the straight line slowly, then decisively.
What's the catch with compounding?
The same mirror math applies to losses: bigger positions mean bigger dollar drawdowns, and gains and losses don't cancel evenly. First the asymmetry: lose 20% and you need a 25% gain just to get back to even, because the recovery is calculated on a smaller base ($1,000 → $800, and $800 needs one-quarter growth to reach $1,000 again). Now watch a choppy sequence. Six winning periods of +5% followed by six losing periods of −5%: fixed sizing gains $50 six times and loses $50 six times — dead even at $1,000. Compounding computes $1,000 × 1.05⁶ × 0.95⁶ = $985.10 — a loss, from a sequence with as many wins as losses, because the −5% hits landed on the enlarged, post-winning-streak balance. Compounding is a snowball in both directions: it grows your gains and it grows the dollar size of whatever losing streak comes next.
