This is a nonrefundable credit. The amount of the credit in any year can’t be more than the amount of tax that you would otherwise pay in any year. If your tax liability is reduced to zero because of other nonrefundable credits, such as the education credits, then you won’t be entitled to this credit.
https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-savings-contributions-save...
https://www.irs.gov/pub/irs-pdf/f8880.pdf
