Working out your break-even
Add the three costs: network gas for the swap (plus an approval if this is the first time you use that token), the pool fee inside the price, and the platform fee. On FBT Swap the platform fee is 0.70% of the input, shown before you sign.
Divide the fixed part — gas — by your trade size. A two-dollar gas cost on a twenty-dollar swap is 10% before anything else. The same gas on a two-thousand-dollar swap is 0.1%.
Why the network choice dominates
Gas is close to fixed per transaction and varies by orders of magnitude between networks. The same swap that costs several dollars on Ethereum mainnet can cost a fraction of a cent on a rollup or a high-throughput chain.
For small amounts, choosing the network is not an optimisation. It is the difference between a viable trade and a donation to block producers.
The costs people forget
The approval transaction is separate and is charged even though it moves nothing. Native-coin gas must already be in the wallet on that network, so a first trade there may need a bridge or a transfer first, each with its own cost.
And a thin pool charges price impact that does not scale down — a small trade into a very small pool can still cost several percent.
When the right answer is not to trade
If total costs exceed roughly 1–2% and the trade is not time-sensitive, accumulating and trading once is usually better than five small swaps. Each swap pays gas again; one larger swap pays it once.
This is also the honest answer to "can I start with ten dollars?" — yes, on a cheap network, and no, on Ethereum mainnet. Stating that plainly is more useful than encouraging a trade that cannot work.