Or you or your spouse are over 65 and get a higher Standard Deduction.
The standard deduction amounts are:
Single 6,350 + 1,550 for 65 and over
HOH 9,360 + 1,550 for 65 and over
Joint 12,700 + 1,250 for each 65 and over
Married filing Separate 6,350 + 1,250 for 65 and over