Hi. I have a return, single person, about 38600 in taxable. Turbotax calc is $3 higher than my Excel calc. How do I see how Turbotax is calculating the tax amount?

At that income level...the tax tables are used...not an exact %.

Sometimes TTX will show a lower tax....IF you have significant Qualified dividends or capital gains, in which case, special tax worksheets are used.

Here's a link that gets you to the IRS PDF of the tax tables

Forms and Pubs Index Search | Internal Revenue Service (irs.gov)