Stimulus checks are landing in the bank accounts of about 80 million taxpayers this week, providing welcome relief to Americans suffering from lost income and jobs. But many are also wondering how the checks — called “Economic Impact Payments” by the IRS — will impact their taxes. “One question is, ‘Will I need to pay taxes on it’?” says Eric Bronnenkant, head of tax at financial services firm Betterment. Taxpayers who haven’t yet filed their 2019 returns are also wondering if they should...