how is the transaction fee calculated?

Question

I've tried Monero-wallet-cli, and following are two transactions:

0.01 XMR by 526 bytes: http://moneroblocks.info/tx/99dae4c9ec68c8b4eb7f9f40a2c01f481d3b979ce97b5e0b2b5f55c759be11f6

0.008 XMR by 3709 bytes: http://moneroblocks.info/tx/9554b072a522e12bf6de27668cfb34cb1351891635ac49c132aeefa3e16bea8d

Why the second transaction is with 0.008 given by 3709 bytes? Which is much larger than 526 bytes. Because monero transaction fee is not calculated by size?

Update:

The first transaction, I used transfer command, and I was actually transferring 0.2 XMR. monero-wallet-cli added another 0.09 xmr, and locked it for a while.

The second transaction I used sweep_all command to transfer all out of my wallet.

thank you :)

Answer 1

The base transaction fee is 0.002 monero per kB. However, change below 0.01 is not retrieved, but kept in the fee, to avoid generating unreasonably small outputs spamming the blockchain, so you may get up to 0.01 extra as the fee in those cases. This threshold is going to decrease soon too (see https://github.com/monero-project/monero/issues/1199).

In your case, both the fees are within 0.01 of 0.002/kB.

Answer 2

It would be nice to see the fee recommendation dynamic generated in the prodocol based on a exponential average of the last 1000 transactions or so, throwing out way-out-of-normal-transactions as to not have a bad actor skewing the average.

What to expect: market prices would be derived fairly, I assume, over time given that there is no TX fee being forced by the network.

Answer 3

This most likely has to do with the recent lowering in fees from 0.01 XMR / kb to 0.002 XMR / kb

Since both of the transactions you referenced seem to be after the fee lowering height, my guess is that you upgraded clients between those two transactions?