The arithmetic
average = (Σ amount × price + fees) ÷ Σ amount
A weighted average of the fills, with the exchange's cut folded into the cost. Buying 0.2 BTC at $62,000 and 0.3 BTC at $58,000 gives 0.5 BTC at a weighted $59,600 before fees.
The larger fill dominates, which is worth stating because it is the mechanism behind most averaging: a second purchase twice the size of the first moves the average two thirds of the way towards the new price.
Why fees are per fill and why that matters
This is the part specific to crypto, and it is why this page exists separately from the stock version.
Exchange fees are charged on every fill, not on the total position. Splitting a purchase into ten pieces pays ten fees. At a 0.05% taker rate that is 0.5% of the position added to your basis — before the market has done anything.
There is a second, less obvious version of the same thing: a single large market order that sweeps several price levels of the book is filled at several prices, and the average is worse than the price you saw when you clicked. The order looks like one purchase in your head and behaves like several here.
The calculator shows the average with and without fees precisely so that gap is visible. On a tight scalp it is the difference between a plan that works and one that does not.
DCA and averaging down are not the same thing
Both produce this arithmetic, and they are different decisions:
- Dollar-cost averaging buys on a schedule, regardless of price. The purchase is decided in advance, so no single buy is a reaction to a loss.
- Averaging down buys because the price fell. The trigger is the loss itself, and there is usually no predetermined limit on how many times it repeats.
The first is a savings method. The second, unbounded, is the first step of a martingale — and in crypto it is more dangerous than elsewhere, because a leveraged position that averages down also moves its liquidation price towards the market with every addition.
The number to recheck afterwards
If the position is leveraged, adding to it changes the liquidation level. The size grew; the margin may not have. Recalculate on the liquidation calculator before assuming the position is in the same shape it was.
On spot, there is no liquidation, but the exposure still grew — and the risk of the combined position is what matters now, not the risk of the original entry.