Why does the rate drop when I increase the swap size

07 September 2026

The rate drops because you are not trading at a single price. The exchanger matches your swap against a stack of limit orders that get more expensive as your size grows.

Most people imagine a swap as a single transaction at a fixed rate. That is true only for small amounts. Once your swap is big enough to eat through several layers of the order book, each successive unit costs slightly more. The average price of the whole swap is lower than the best available rate you saw when you started.

Here is how the mechanism works.

The order book is a ranked list of sell orders. The cheapest Bitcoin sits at the top. Below it are progressively more expensive offers. When you swap into Bitcoin, the exchanger takes the cheapest sell first. If your swap is larger than that single order, the exchanger moves to the next cheapest, then the next. Each deeper layer has a higher price. Your average rate is the weighted mean of all those layers. The deeper you go, the more the average is pulled toward the higher prices at the bottom of the stack.

This is not a penalty or a hidden fee. It is the same structure that exists on every honest exchange. A small swap touches only the top layer. A large swap consumes multiple layers. The rate you see quoted for a small test amount is the rate for the first layer alone. That rate cannot hold for a larger swap because the first layer is too thin.

How thin? It depends on the pair and the moment. On a liquid Bitcoin market the top layer might be a fraction of a Bitcoin. On a less liquid token the top layer could be a few hundred dollars worth. In either case, once your swap exceeds that amount, you begin moving down the book.

The effect is not linear. If the order book is steep - meaning the price jumps sharply between layers - your rate drops faster. If the book is flat, with many small price increments, the drop is gradual. You cannot know the shape of the book without looking at it, but you can infer it from how much the quoted rate changes when you adjust your swap size by a small amount.

There is also a psychological component. Large swaps sometimes trigger the exchanger’s spread-widening logic. The exchanger does not know whether you are a savvy trader or someone who just clicked a button. To protect itself from front-running and adverse selection, it may widen the spread for larger amounts. That makes the rate worse even before the order book mechanics take effect.

You can test this yourself. Start a swap for a small amount and note the rate. Double the amount. The rate will almost certainly be worse. Double it again. The pattern continues until the swap is large enough that the exchanger starts working the order behind the scenes, slicing your order into smaller pieces to avoid moving the market against you. At that point the rate may stabilise, but it will be lower than the rate for a tiny swap.

The core fact is simple: rate and size are coupled. There is no single price for Bitcoin. There is a price for the first tenth of a Bitcoin, a different price for the next tenth, and so on. Your swap size determines how many of those prices you have to pay.

If you want to understand the full picture of how large swaps behave, read the page When your swap is big enough to move the rate. That page covers what changes when your swap is large enough that the exchanger itself has to adjust its behaviour, not just consume deeper layers of the book. The two mechanisms - order book depth and market impact - are related but distinct. This page is about the order book. That page is about the moment your swap becomes a market event.

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