Originally Posted by IADFlyer123

This means that you will need 80,000 miles minimum to book a roundtrip economy class ticket at the lowest/ saver rate. Seats in this category are capacity controlled and may not be available at all times.

The 85000 one way or 170,000 round trip is for last seat availability or any seat available in economy. This is the standard price. This is only applicable if the saver rate is not available.

So with your 50,000 mile balance, the miles are only enough for a one way trip to Japan at the lowest rate - if the seats are available at that rate. It is better you use money to buy your ticket.