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Blockchain.info gives you the options of 'frugal', 'normal' and 'generous' for setting miners fees and leave it slightly vague as to what the transaction fee will ultimately be.
I want to use their Make Outgoing Payments API to send payments but how can I know what they choose as a transaction fee?
What if I have 0.01 BTC in my wallet and want to send it all to an address. There won't be enough BTC left over for a fee. What happens then?
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There really isn't a standard fee value. Various clients implement different amounts. For example on my MultiBit installation it's currently set to 0.0001 BTC per 1000 bytes of transaction size.
You must include a fee otherwise miners won't confirm your transaction.
For Blockchain.info's case, using their API, if you don't have the $fee parameter, Blockchain.info will automatically add 0.0005 BTC in fee, which is the default value.
All transactions include a 0.0005 BTC miners fee.
So if you send 0.01 BTC with their API, and don't specify the $fee parameter, it will add a 0.0005 fee to your transaction.
EDIT This means you actually need at least 0.0105 BTC (0.01 + 0.0005) in your wallet to make the transaction. If you want to send all of the 0.01 BTC, you have to actually send 0.0095, otherwise the transaction won't go through.
The API docs say all transactions include a 0.0005 BTC miners fee by default however the Account->Settings->General says they 'Follow the fee policy suggested by the mainline bitcoin client' if you select 'Normal' Default Fee Policy. I guess that must also be 0.0005 BTC or would it depend on the transaction size in bytes and in BTC? – Dan – 2014-02-12T15:03:56.960