Why does a crypto swap ask for an exact deposit amount?
Because on many services the amount is what identifies your payment. When a deposit address is shared between customers, the address alone cannot say whose money arrived — two people sending 344 USDT to the same address produce two chain entries that look identical. A distinct amount is what separates them.
Not every service works this way, and the same service may not work this way for every asset. What follows is the general mechanism first, then what SwapToZec actually does.
Two ways to attribute a deposit
A service receiving your coins has to answer one question: which order is this payment for? There are three common answers.
| Method | How it identifies you | Used when |
|---|---|---|
| Destination alone | The place you sent it to | A fresh destination per order is practical |
| Destination + tag | A tag or memo you include | The network provides such a field |
| Destination + amount | The exact figure you send | One destination serves several orders |
Only the third makes the amount load-bearing for identification. Under the first, a rounded figure would still be identified — though it would then be classed as an underpayment or overpayment, which is its own problem.
On SwapToZec
You do not need to work out which case applies to you. Your swap page states exactly what to send, where to send it, and — on the networks that use one — the tag or memo to include. Following that screen is the whole requirement.
Three things are worth knowing:
- Send the figure exactly as displayed, including every decimal place. Do not round it.
- If a tag or memo is shown, it is required, not optional. A payment arriving without it cannot be processed automatically.
- The deposit figure can differ slightly from your original quote — always downward, never by more than a fraction of a cent. It is not a fee and nothing is kept.
Why the last digits sometimes look odd
The figure on your deposit screen may end in digits that look arbitrary — 344.000037 rather than a tidy 344. That is deliberate and it is the number to send. It is not a rounding error, not a hidden charge, and not something to clean up before sending.
If you round it, the deposit has to be checked by hand before the swap can proceed, which is slower than sending the exact figure would have been.
What happens if the amount is wrong
SwapToZec compares the deposit to the expected figure exactly, in the smallest unit the chain has. There is no tolerance band. A deposit one atomic unit short is short.
Underpayment
A deposit smaller than expected stops and waits for a person. It is not processed at a reduced rate automatically, and it is not automatically refunded. Contact support before sending anything further, rather than guessing at a top-up.
Overpayment
A deposit larger than expected also stops for review. The surplus is not credited automatically, and the swap does not proceed with the extra.
Rounding
Rounding the figure to something tidy is the case this cannot absorb. Where the amount forms part of the identification, a rounded number may match nothing at all — or worse, match something it should not. Either outcome needs a person to resolve, and both take longer than sending the figure as displayed.
No refund is automatic on SwapToZec. Where a refund is appropriate it is arranged by an operator, and it needs a refund address. That is why the deposit screen asks for the figure it shows rather than something close to it.
Network fees and what actually arrives
What matters is the amount that lands at the deposit address, not the amount you typed into your wallet.
The two differ depending on how your wallet or exchange handles fees:
- Sending from your own wallet on most chains, the network fee is paid in the chain's native coin and on top of the amount sent. The full figure arrives.
- Sending from an exchange, many deduct the withdrawal fee from the amount. Ask for 344 and 343.x arrives — an underpayment.
- Sending a token, the fee is usually paid in the native coin (ETH, BNB, TRX, SOL), so the token amount is unaffected — but you need some of that native coin to send at all.
If you are withdrawing from an exchange, check whether the figure you enter is the amount sent or the amount received, and set it so the displayed figure arrives.
Before you send
- Copy the amount from the deposit screen rather than retyping it.
- Do not round it, even when the trailing digits look like noise.
- Check whether your sending platform deducts its fee from the amount.
- Send one payment rather than several. Multiple deposits to one swap are a review case.
- Send on the network named on the instruction — the address does not tell you the network.
Related
Once your deposit is broadcast, the next question is how long it has to settle — see how on-chain confirmations work. If a timer ran out somewhere in the process, what "expired" means on a swap covers which clock ended and what it affects.