PHP: how to calculate the transaction fee?

[DaMan]

Hi!

I have a big problem i can't solve by myself:

I am using PHP and use the API "sendfrom" command to send some transactions.

Is there a way to calculate the exactly needed transaction fee? I tried it with a basic 2% calculation and if I send i.e. 2 BTC I check if my account balance is more than 2 BTC + 2%.

But if I am sending more transactions it results in an error, because the account balance is to low.

Is there a way/command to calculate the correct transactions fee needed for each transaction? Or a way to get the transaction KB value?

Kind regards,

DaMan

[1715089869]

1715089869

[1715089869]

1715089869

[winnetou]

Have you found a solution for your problem?

[talpan]

Hi!

I have a big problem i can't solve by myself:

I am using PHP and use the API "sendfrom" command to send some transactions.

Is there a way to calculate the exactly needed transaction fee? I tried it with a basic 2% calculation and if I send i.e. 2 BTC I check if my account balance is more than 2 BTC + 2%.

But if I am sending more transactions it results in an error, because the account balance is to low.

Is there a way/command to calculate the correct transactions fee needed for each transaction? Or a way to get the transaction KB value?

Kind regards,

DaMan

There is currently no way to calculate the resulting fees, afaik.

[arsenische]

There is currently no way to calculate the resulting fees, afaik.

but bitcoin software does it somehow.. probably just need to look at sources

[maaku]

What fee it calculates depends on what transaction outputs it decides to use to fund the new transaction, and (I could be wrong with this point) I don't believe it does so deterministically. So there certainly isn't a way to do it without all the information in wallet.dat, and that might not even be enough.

[Pieter Wuille]

What fee it calculates depends on what transaction outputs it decides to use to fund the new transaction, and (I could be wrong with this point) I don't believe it does so deterministically. So there certainly isn't a way to do it without all the information in wallet.dat, and that might not even be enough.

This is correct.

I believe the solution is providing an RPC call that creates a preliminary transaction (which isn't broadcast yet), but can be inspected. At this point, it can either be committed (broadcast) or reverted through another RPC call.

[kjj]

What fee it calculates depends on what transaction outputs it decides to use to fund the new transaction, and (I could be wrong with this point) I don't believe it does so deterministically. So there certainly isn't a way to do it without all the information in wallet.dat, and that might not even be enough.

This is correct.

I believe the solution is providing an RPC call that creates a preliminary transaction (which isn't broadcast yet), but can be inspected. At this point, it can either be committed (broadcast) or reverted through another RPC call.

Yup, but it needs to lock all transactions involved in the potential spend until it gets approval / rejection / timeout.  For almost all systems that I can think of, this is worse than just paying the fee and noting the amount later.