Is there a reason someone wouldn’t get the full Earned Income Tax Credit?

The EIC is calculated on a bell curve----the amount you get goes up or down with the amount of income you earned from working.   It is not just a flat "full" amount.

https://ttlc.intuit.com/questions/1899157-what-are-the-qualifications-for-the-earned-income-credit-eic-or-eitc

https://www.irs.gov/credits-deductions/individuals/earned-income-tax-credit/use-the-eitc-assistant

TurboTax evaluates your tax return and applies it to any credit you may be entitled to.

The Earned income credit has several conditions that are required to qualify for the credit.

If you're not claiming a qualifying child:

• You (and your jointly filing spouse) can't be claimed as a qualifying child or dependent on anyone else's return.
• You must be at least age 25 but under
• You must have earned income.
• You must be a US citizen or resident alien for the entire tax year.
• You must have a valid Social Security number 
  • (not an ITIN) for yourself, your spouse (if filing jointly), and any qualifying children on your return.
• You can't have investment income exceeding $11,000.
• You cannot file a Form 2555 or 2555-EZ (Foreign Earned Income)
• You are required to file a return with 
  • Single,
  •  Married Filing Jointly, 
  • Head of Household, or 
  • Qualifying Surviving Spouse filing status, even if you're not required to file a return.

In addition, both your earned income and Adjusted Gross Income (AGI) may not exceed:

• $17,640 if you're not claiming a qualifying child ($24,210 if filing jointly).
• $46,560 if you're claiming one qualifying child ($53,120 if filing jointly).
• $52,918 if you're claiming two qualifying children ($59,478 if filing jointly).
• $56,838 if you're claiming three or more qualifying children ($63,398 if filing jointly).

You can preview your tax return by going to:

1. On the menu bar on the left that shows.
2. Select Tax Tools
3. On the drop-down select Tools
4. On the popup menu
5. Select View Tax Summary
6. On the left sidebar
7. Select Preview my 1040.
8. Schedules 1,2&3 are included if you scroll down past your 1040.
9. To return to the entry screens press Back on the sidebar.

Some key numbers on your 1040 tax return are:

• line 1z - earned income
• Line 11 - Adjusted gross income.