I attached a samplefile.

I want a field to update based on the last portal entry. I have created a relationship to isolate the last portal record. If I create a calculated field it works fine. However, I would rather a regular field that autoenters with the same calculation. The reason is simple. The field will usually but not always be based on the last portal and the user may need to override the calculation. Please take a look.

test.fp7.zip

It generally doesn't work when you base an autoenter calculation on a related field, because Filemaker only triggers the calculation when is sees changes in the current record. I suggest that you use a calculated field, and then create an additional field where the user can enter an overriding value. If you superimpose the two fields, then they will appear to be a single field and will work as you want. See the attached file. Also have a look at how the field behavior is set up for both fields.

test.fp7.zip