Where do I look to see why a $315 tax credit is being given on what should be a simple return?

We cannot see your screen or your tax return.  One guess----did you have a contribution to an employer retirement account in box 12 of your W-2?   You might be getting the retirement saver credit.

I suggest you preview your tax return to see what credits you may have gotten.

You can preview your tax return by going to:

1. On the menu bar on the left that shows.
2. Select Tax Tools
3. On the drop-down select Tools
4. On the popup menu
5. Select View Tax Summary
6. On the left sidebar
7. Select Preview my 1040.
8. Schedules 1,2 & 3 are included if you scroll down past your 1040.
9. To return to the entry screens press Back on the sidebar.

Lines 27, 28 & 29 are the most common credits.

I expect you may have gotten the Earned Income Credit listed on line 27.

Some key numbers on your 1040 tax return are:

Line 15 - Taxable Income

Line 24 - Total Tax.

Line 25 d - Withholdings.

Line 26 - Estimated tax payments

Line 33 - Payments including Credits.

Line 34 - Overpayments.

Line 37 - Tax owed.