The credit limit worksheet includes other nonrefundable credits besides what is found on Line 19 of Form 1040. The missing $500 may be coming from one of these credits:
- Foreign Tax Credit, nonrefundable childcare credits and education credits, saver's credit found on Schedule 3 Lines 1 - 4
- Other less common credits found on Schedule 3 Lines 6d through 6g and 6l
- Residential energy credits found on Form 5695 Line 30
Since these credits are "use it or lose it" and the adoption credit carries forward, your adoption credit is used last and the remainder carries forward if you have one of these to reduce your tax this year.
