It's estimated due to the way bitcoin works. A transaction can be made up of a different number of inputs, if the inputs don't exactly match the output (the am

It's estimated due to the way bitcoin works. A transaction can be made up of a different number of inputs, if the inputs don't exactly match the output (the amount you want to send), there is "change". The change is sent to a new address (belonging to the sender). So blockchain.info and this site are guessing as to which of the outputs was the intended sending amount and which was the change.