when you are sending bitcoin, you have to pay a fee. and the fee is calculated based on the size of your transaction in bytes.
depending on how many translation outputs (the transactions you have received that sum up to this 0.0012
BTC) your transaction size changes.
if it is one then your transaction is most probably around 226 bytes and you will have to pay 0.0002-0.0003
BTC fee for it.
you can play around here to see how things work with fee:
https://coinb.in/#fees (thanks to @TryNinja in another topic)
