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Topic: Why some transaction have send btc to same address? (Read 345 times)

staff
Activity: 3374
Merit: 6530
Just writing some code
That output is the change output. Inputs are spent in full, so the amount that isn't in the output for the intended recipient must be sent to a different output that the sender controls. That other output is the change output. It is like paying for a 10$ item with a 20$ bill; you receive back to yourself 10$ in change.
newbie
Activity: 22
Merit: 0
Hello

I wonder why some wallet systems send btc back to same address.

If you look to this transaction https://www.blocktrail.com/BTC/tx/5d13332abbdff9bbea02426ddaa82418e2071d91562ba999c2a8f102bd95f559 you see the input is the same address like the output last line.
Not every transaction have this but I tried blockIo and it has also same address as output.

This transaction has no same output address https://www.blocktrail.com/BTC/tx/91678f7a2452d5bc5f8164003509354397da92be6b438e8d3e30a473878722ce

Why that? Does it not make the miners fee higher?

EDIT: I am asking this because I want to calculate estimate transaction size + fee but I cannot if output is sometimes one more or one less
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