It said I got a earned income credit of $250 bringing my return to 900 then in the end my return is 670 can you explain why I lost the credit please

No, I can't say exactly why your refund went from $900 to $670, since we can't see your tax return. However, your refund amount goes up and down as you go through the TurboTax interview questions.

• Perhaps, TurboTax wasn't done with all the calculations when you saw the $900 refund. 
• Perhaps, you no longer qualify for the Earned Income Credit or you qualify for a lower amount.

To qualify for and claim the Earned Income Credit you must:

• Have earned income; and
• Have been a U.S. citizen or resident alien for the entire tax year; and
• Have a valid Social Security number (not an ITIN) for yourself, your spouse (if filing jointly), and any qualifying children on your return; and
• Not have investment income exceeding $3,600; and
• Not be filing a Form 2555 or 2555-EZ; and
• File a return with the Single, Married Filing Jointly, Head of Household, or Qualifying Widower 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:

• $15,570 if you're not claiming a qualifying child ($21,370 if filing jointly);
• $41,094 if you're claiming 1 qualifying child ($46,884 if filing jointly);
• $46,703 if you're claiming 2 qualifying children ($52,493 if filing jointly);
• $50,162 if you're claiming 3+ qualifying children ($55,952 if filing jointly).

One more thing — if you're not claiming a qualifying child:

• You (or your jointly filing spouse) must have been born on or after January 1, 1955; and
• You (or your jointly filing spouse) must have been born on or before December 31, 1994; and
• You (and your jointly filing spouse) cannot be claimed as a qualifying child or dependent on anyone else's return.

Phew! Got all that? Fortunately, TurboTax handles the behind-the-scenes calculations so you don't have to.

To visit the EIC section, search for EIC in TurboTax and select the link in your search results. However, don't do this until after you've entered all your income and personal information — otherwise you'll get an incorrect EIC calculation.

Source: TurboTax FAQ and Video