What a swap rate is made of
When you see "1 BTC ≈ X ETH" in a swap form, three things are inside that number:
- The source quote — the price at which a liquidity provider or market maker will actually do the trade for that pair and size right now.
- The spread — the service's margin, applied to the quote.
- The payout fee — the network cost of sending you the output coin, subtracted from the output.
Different services differ in all three, and most of the difference between a good rate and a bad one is in the first: which source was asked, and whether it was the best one available for this pair at this size.
What the routing does
SyntheticSwap does not have one liquidity source. For each quote, the swap engine asks the available sources for the pair and amount, normalises the answers to an all-in figure (spread and payout fee included) and returns the best one. This is done automatically at quote time, not on a fixed schedule, and is the part of the system we describe as AI-powered routing: the choice of source adapts continuously to which one is offering the best net output for the request, instead of relying on a single provider whose pricing may be good for BTC/ETH and poor for XMR/USDT.
Two practical consequences:
- Thin pairs benefit most. On a deep pair like BTC/USDT every source is close; on a pair like ZEC/USDT or XMR/USDT the difference between sources can be several times the spread.
- Size matters. A source that is best for $100 is not always best for $20,000, because each has its own depth. The routing re-evaluates per request.
What is — and is not — in the number you see
The estimate in the form is the amount you will receive, after spread and payout fee. It is not a "market rate" from which fees are later deducted. That is deliberate: the only number that lets you compare services is the output amount, and the only number that matters to you is the same one.
What is not in the estimate is the fee you pay to send the deposit — your wallet sets that — and any movement of the market between the estimate and your deposit confirming, because the rate is floating.
The transparency check on every pair page
Each core pair page fetches a live quote for a sample amount and compares it with the CoinGecko mid-market rate for the same pair. The result is shown as a single percentage: how far the all-in output is from the theoretical mid-price. The mid-price is not achievable by anyone — every venue has a spread — but the percentage is the honest measure of total cost, and it lets you see at a glance when a pair is expensive (thin liquidity, high payout-chain fees) and when it is not. Check BTC → USDT (TRC-20) against XMR → USDT (TRC-20) to see the difference between a deep pair and a thinner one.
Why the same pair is cheaper at $2,000 than at $50
The payout fee is a fixed amount in the output coin. Paying out USDT on TRON costs cents; paying out ETH or an ERC-20 token costs an Ethereum transaction; paying out Bitcoin costs a Bitcoin transaction. That fixed amount is a large percentage of a small swap and a negligible percentage of a large one. The spread, by contrast, is proportional. So:
| Swap size | Dominant cost | What to do |
|---|---|---|
| Small (tens of dollars) | Payout fee | Choose an output coin with a cheap network — USDT on TRON rather than ERC-20 — or combine small swaps into one |
| Medium (hundreds to low thousands) | Spread | Compare the all-in output; routing quality decides |
| Large (tens of thousands) | Liquidity depth | Split across two or three swaps if the maximum is hit; watch drift on slow deposit coins |
How to compare two services fairly in two minutes
- Pick the same pair and the same input amount on both.
- Read the output amount — not the rate, not "0% fee" claims. If a service shows a rate and then a separate fee, do the subtraction.
- Check whether the output includes the payout network fee. If it does not say, assume it does not, and ask.
- Check what the rate is — floating or fixed — and when it locks. A fixed rate that is 1% worse is not "worse" if you need certainty; it is a different product.
- Check the minimum: a service that looks cheap may not accept your amount.
If both services show an all-in output, the higher number wins. Everything else is marketing.
Where the rate is honestly worse
There are situations where no routing helps, and it is better to know them:
- Very small amounts on expensive payout chains. Ten dollars into an ERC-20 token pays an Ethereum fee that may be most of the ten dollars. Use TRON, Solana or Polygon rails for small stablecoin amounts.
- Illiquid pairs. Some coins have one or two viable sources. The routing picks the best of them, but "best" can still be a wide spread.
- Extreme volatility. Sources widen spreads when the market moves fast, and a floating rate on a slow deposit coin adds drift on top.
- Deposits near the maximum. Depth is finite; the last part of a large order costs more than the first.
Frequently asked questions
Is there a hidden fee? No. Spread and payout fee are inside the estimate; your sending fee is outside it because your wallet sets it.
Why did I receive slightly more or less than the estimate? The rate is floating and locks at deposit confirmation. Fast deposit coins keep the difference within the one-minute refresh; Bitcoin at a low fee can drift more. The floating vs fixed guide explains how to keep it small.
Do you match a competitor's rate? There is no manual matching — the routing picks the best available source per request. If you see a materially better all-in output elsewhere for the same amount, that is useful information; tell us which pair.
Do rates differ by amount? Yes, for the reasons above. Always quote with your real amount.
Where do I see the live limits and cost? On every pair page — the pairs list links to all of them.
BTC → USDT (TRC-20)
ETH → USDT (TRC-20)
USDT (TRC-20) → BTC
XMR → BTC