How do I calculate amount I used on medical expenses, from 401K early distribution/loan offset, to avoid paying the 10% penalty?

@dmertz Is Loan offset eligible for 10% penalty exception?

Yes.  A penalty exception, if one has one, can be applied to any early distribution.

What do I factor into the medical amount?
Out of pocket spent for 2018?
Medical bills at the time of the distribution?
Or medical bills paid after the distribution?

Amounts paid out of pocket in 2018.  The amount of those expenses that exceeds 7.5% of AGI can be claimed as a medical expense exception to the early-distribution penalty.  It's the amount that would have appeared on Schedule A line 4 if you itemized deductions.

I'm using standard deduction, not itemized. Does the exception apply to both or just itemized?

The exception applies whether you itemize or not.  It just so happens that the amount on which you can claim this exception is the same as the amount that would appear on Schedule A line 4 if you *did* itemize.

Thank you for the information.

When you enter your 1099-R, you will answer a number of interview questions that will lead you to the screen below in the screen shot.

screenshot?