At Zaif, the actual fee paid to miners is not the amount set by you when requesting a withdrawal,
but a rate relative to the transaction size (fee per 1kb).
As such, the actual fee paid in the network becomes different from the the withdrawal fee.

When it comes to bitcoin withdrawals, it is said that the fee should be relative to the transaction size,
and we at Zaif agree with this.

This is because bitcoin mining is done in block (limited to 1MB as of March 2016) units
and miners try to maximize fee per block.

As of March 2, 2016, the withdrawal fee from Zaif
is paid as a fee per 1kb at a rate of twice the withdrawal fee received.
At present, this means that approval can be expected within 2-3 blocks depending on your settings,
but please understand that this is not something we can promise.
Moreover, we plan to change the scale factor depending on the situation in the bitcoin network.

[Real example]
When using the default withdrawal fee of 0.0002 BTC and the block size is the smallest 225 bytes,
the miner’s fee is calculated as 0.0002*2*225/1000=0.00009BTC. In this case, the difference is not returned.
If the block size is bigger than 1kb, the miner’s fee will also become higher than 0.0002 BTC,
but you will of course not have to pay any additional charges.

The actual block size is determined during the withdrawal process,
so it’s unknown when we first receive your withdrawal request.