I know there is a formula for determining whether or not to use your mileage to buy a ticket vs. the actual cost of the ticket, but I can't find it. Can anyone help me out with this? I need to go from DTW to AMS in July and the cost of the ticket is approx. $1200. Alternatively, I could burn up 100k ff miles from my NW account. Am I better off using the mileage for the ticket or just buying it outright? The fees and taxes on the award ticket amount to approx $75.

Very common question...no one-size-fits-all answer. For starters, search this board and the NW board - others have asked similar questions and there are lots of good arguments for both the redemption and for buying the ticket.

It depends greatly on your current cashflow, "milesflow", pursuit of elite status on NW, future plans for miles, etc. To some, taking 1.2 cents per mile and keeping $1200 invested is a great call. To others, they'd buy the ticket, earn some more miles, and hold out for closer to 2 cents per. It's a very individual decision.

This board will give you the general arguments for/against redemption; the NW board might yield some tips/tricks on the program itself: routings that might save you some miles, earn you more bonus miles, partner redemption possibilities, etc.

Welcome to FT!

As mentioned above there is no one size fits all answer.

If you are getting a first/business class ticket for 100K miles, then I would say that it is worth using the miles. If you are getting a coach ticket then it depends.

Also if your dates are flexible, try to see if you can get a standard award in one direction at least. That will cost you fewer miles (or give you a better cabin). There are some dates in July for which standard awards are available (in either coach or business) for DTW-AMS.

I show you the math on the Value of Miles page of my website below.