Question about transactions

Watching the videos of the bitcoin 1.0 course I realized that every time I spend bitcoins, my wallet builds a transaction using the utxos that I can spend.
I ask the question with an example:
My wallet previously received 1 btc and 0.5 btc respectively in 2 different transactions.
If I want to send 1.2 btc to an address, my wallet will take my 2 utxo (1 + 0.5) and build a transaction in which it will send 1.2 btc to the desired address and 0.3 btc back to me?.
Instead, if i want to send 0.5 btc to an address, would my wallet take the 0.5 utxo and send only that?
In this second hypothesis, would I pay less fees than the first being the tx more simple?

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If you would send 0.5 including the fees then you would only spend that output. You would pay less because you would be taking less space in the block. Remember bitcoin network does not care how big your transaction is in bitcoins, rather how much space you will be taking in a block.(satoshi per byte) Check this fee calculator:

The more inputs and output you have the larger the transaction will be, thus making you pay more fees as they are calculated satoshi per byte.

Check that site if you are still confused as it has a nice visual representation.
Hope that helps.

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All clear! Many thanks!!
now another question arises, always with a practical case:

  1. I am a miner and I own a newly mined btc and send it with a transaction (1 btc tx).
  2. I purchased fractions of bitcoins in multiple transactions for a total of 1 btc and send it in one transaction (always 1 btc tx)
    In the first case, will I pay less fees than in the second case right?
    Since in the second case my transaction will have multiple inputs.
    Let me know if I say right …
    Thanks so much
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Yes you will pay less as in the first option you would only have 1 input and 2 outputs.


If you would to the first case at the current time the fee would be: 14690 satoshi
If you would have 10 inputs it would be: 101270 satoshi
(Does fees are current fees for today if you want your transaction to be included in around 60 minutes.)

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I understand…Thanks.
Another question:
If I wanted to transfer funds between 2 of my wallets, without haste (even if the operation was performed the next day it doesn’t matter), is there a way to set a low fee in the transaction (i.e. with trezor wallet)?.

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If the wallet you are using supports setting custom fees then yes. If we take a look at this website again and set it to legacy with 2 inputs and 2 outputs and then choose the transaction to be included in 480 minutes the total fee would be 7 cents. It would take around 8 hours for a miner to pick it up. Keep in mind that does are estimates and if you set a low custom fee your transaction may take days to get confirmed.

Thanks a lot…I see from the web page that Trezor support custom fees…i’ll try then i’ll let you know.
Thanks again

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Sounds good. Glad I could help you out.