When calculating the earned income credit, turbo tax asks if I want to calculate it using my 2019 income. When using the 2019 income, my credit is larger. Is this legal ?

[SweetieJean]

Yes.  It was part of the Taxpayer Certainty and Disaster Tax Relief Act of 2020.

Earned Income Tax Credit (EITC) | Internal Revenue Service (irs.gov)

[RayW7]

For tax year 2020, the CAA allows taxpayers to use their 2019 earned income if it was higher than their 2020 earned income in calculating the Additional Child Tax Credit (ACTC) as well as the Earned Income Tax Credit (EITC).

-follow this link for more information-

Earned Income Credit - TurboTax Tax Tips & Videos