# Starting descent

After I use the (Cruising altitude/1000) x 3 formula to calculate top of descent, should I subtract the airport elevation from the result?

I always just use fpltoif.com, it tells you everything you need to do and it does it for free.

Well, there’s a few different ways to solve for this and it depends on what you’re doing.

First of all, don’t add the airport elevation. The formula you used is for solving distance from the airport and had nothing to do with field elevation.

If you’re descending via a STAR, it will have altitudes assigned you different fixes, so just subtract the flight level of the fix from your current flight level and divide by 3.

You can also just try to be at 10000 AGL 25nm from the field. This can be solved by taking your current flight level and subtracting 100 (add the flight level of the field elevation) then dividing by 3. Then add 25 to that.

Thank you very much

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