At $48,450 in box 1 of the W-2 when Married filing Jointly (which produces an income tax liability of $2,298), each spouse's credit is equal to only 10% of the first $2,000 of retirement contributions. That's a maximum of $200 of this credit per spouse. Line 20 is showing more than $400, so it appears that there is some other credit on Schedule 3 as well (the foreign tax credit?).
With just $1,500 contributed to retirement, the maximum possible for this credit is $150 under these circumstances.
