TT is calculating the Saver's Credit (Retirement Savings Contribution Credit) at $453 on $7000 IRA. How is that 0, 10, 20, or 50%?

You AGI may be too high to receive the full credit, see the phase out amounts below.   Or, your tax liability was only $453.   Depending on your adjusted gross income and tax filing status, you can claim the credit for 50%, 20% or 10% of the first $2,000 you contribute during the year to a retirement account. Therefore, the maximum credit amounts that can be claimed are $1,000, $400 or $200.

• The biggest credit amount a married couple filing jointly can claim together is $2,000.
• But, if you and/or your spouse took a taxable distribution from your retirement account during the two years prior to the due date for filing your return (including extensions), that distribution reduces the size of the Savers Credit available to you.
• The Savers Credit is a 'non-refundable' tax credit. That means this credit can reduce the tax you owe to zero, but it can't provide you with a tax refund.

In 2020, the maximum adjusted gross income for Savers Credit eligibility is:

• $65,000 for a married couple filing jointly,
• $48,750 for a head of household, and
• $32,500 for all other taxpayers.

The maximum credit you can claim phases out as your income increases.  To see the phase out amount, click that link.

If you are receiving any of this credit, that credit will be 10%, 20% or 50% of your retirement contributions (reduced by the amounts of any distributions in recent years), but not any more than the amount that reduces your income tax liability to zero.  This is a nonrefundable credit.  My guess is that your income tax liability without this credit would be $453, so, if this is the case, this credit cannot exceed $453.

This credit does not phase out, it is instead reduced stepwise based on AGI and filing status determining which percentage is to be applied to your first $2,000 of contributions.