Keep BTC Aside for Your Next Bitcoin Fee

To leave BTC for a later Bitcoin fee, keep at least one spendable BTC output in your wallet instead of sending your whole balance. A Bitcoin network fee is paid in BTC, so a token or bridged version of Bitcoin on another network cannot cover it.

This matters when you move funds between networks. For a fuller explanation of how Biswap’s Polygon-to-Bitcoin route works, see the route’s mechanics; the key point here is that BTC on Bitcoin and a representation of BTC elsewhere are not interchangeable for paying a Bitcoin fee.

How much BTC should you leave behind?

There is no fixed reserve that fits every future transaction. The fee depends on how much transaction data you send and the fee rate you choose, usually shown by a wallet in satoshis per virtual byte.

A transaction that spends several separate outputs can take more space than one that spends a single output. A busy fee market can also make a higher fee rate useful if you want the transaction confirmed sooner. Your wallet’s fee estimate gives you a practical guide, but the future fee may differ from today’s.

For a simple transfer, leave enough BTC to cover the kind of transaction you expect to make next, with some room for a higher fee rate. If you do not know what that transaction will be, keeping a separate output with a modest reserve is more useful than trying to guess an exact number of satoshis.

What does a separate BTC output do?

A Bitcoin wallet spends unspent transaction outputs, or UTXOs, rather than drawing from one account balance. You can think of each output as a separate piece of BTC that can be used as an input to a later transaction.

When you spend an output, the transaction uses it in full and sends any leftover value back to you as a change output, if the wallet creates one. A wallet may combine multiple outputs to meet the amount you are sending, which can also raise the transaction’s size and fee.

Before sending, check that the wallet has left your reserve output unspent. If you send your full balance, or the wallet selects the output you meant to save, you will need to receive more native BTC before you can make another Bitcoin transaction.

How can you check the reserve before sending?

Review the wallet’s selected inputs and the amount it will send before you approve the transaction. Some wallets manage coin selection for you, while others let you choose which outputs to spend.

• Keep the reserve in native BTC on the Bitcoin network.
• Check which outputs the wallet plans to spend.
• Review the fee rate and estimated fee for the transaction.
• Confirm that any change returns to an address you control.

Do not count a bridged BTC token toward this reserve: it may represent Bitcoin’s value on another network, but it cannot pay a Bitcoin network fee. The useful habit is to decide what you need to keep before entering the send amount, then check the wallet’s input selection and fee estimate before you confirm. Those are the signals to watch on your next transfer.