What is 2020 tax on $76000 AGI married filing jointly

The tax is on your taxable income which is the AGI - the Standard Deduction or Itemized Deductions.  And it depends on what kind of income you have.  Like if you have any qualified capital gains or dividends those are taxed at a different rate.  I think the Standard Deduction for Joint is 24,800 so your taxable income would be $51,200.

Put your income information into the software so the software can use your filing status, your dependents (if any), tax withheld, credits and deductions, etc etc. etc.  The software really needs lots of updates before you get reliable results but you can see a "ballpark" amount.  

Found this page.  It has the tax rates listed

https://www.irs.com/articles/2020-federal-tax-rates-brackets-standard-deductions/