Transaction fee depend upon size and size depends upon number of input and number of output.
When you will send 0.5 bitcoin from one address which have received 1
BTC in single transaction before than it will have one input + two output which is also considered as normal bitcoin transaction and it have 226 bytes.
If you have received bitcoin in very small quantity before in many micro trasnaction and want to send it all to another address you will have multiple input so your tx size will increase as well as your fee.
Learn more about tx fee here
http://bitcoinpam.com/bitcoin-transaction-fees/https://en.bitcoin.it/wiki/Transaction_fees