Your deductions reduces the amount of taxable income you have thus, the taxes you pay also reduces. As for the credits, there are two types of tax credits: refundable and non-refundable credits. Non-refundable tax credits would reduce your tax payable at a maximum of $0 it doesn't generate a refund. On the other hand, refundable tax credits would generate a refund, if your tax credits exceeds the total tax payable. Therefore, if you have several reductions your tax payable would decrease and by having refundable tax credits you maybe able to get a refund.
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