What is the maximum contribution/tax credit for a Roth IRS for a couple: married filing jointly?

This, from IRS:

For 2015, 2016, and 2017, your total contributions to all of your traditional and Roth IRAs cannot be more than:

• $5,500 ($6,500 if you’re age 50 or older), or
• your taxable compensation for the year, if your compensation was less than this dollar limit.

The table in the link below shows you your income limits for married filing jointly (MFJ).

https://www.irs.gov/retirement-plans/plan-participant-employee/amount-of-roth-ira-contributions-that...

In order to qualify for the 2016 Retirement Savings Credit, you must meet all four of these requirements:

- You are not a full-time student.
- You were born on or before January 2, 1999.
- No one else claims you as a dependent on their tax return.
- Your adjusted gross income (AGI) does not exceed:
-----$61,500 if married filing jointly
-----$46,125 if head of household
-----$30,750 if single, married filing separately, or a qualified widow(er)

And have eligible contributions.  These include:

Contributions to a traditional or Roth IRA,
Salary reduction contributions (elective deferrals, including amounts designated as after-tax Roth contributions) to:
A 401(k) plan (including a SIMPLE 401(k)),
A section 403(b) annuity,
An eligible deferred compensation plan of a state or local government (a governmental 457 plan),
A SIMPLE IRA plan, or
A salary reduction SEP, and
Contributions to a section 501(c)(18) plan.

https://www.irs.gov/pub/irs-pdf/f8880.pdf