On a joint tax return there is only one MAGI that is the total of all income from both spouses.
For 2015, 2016, 2017 and 2018, 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.
(Taxable compensation is generally wages that you worked for - W-2 or net self-employed income minus the deducible part of the SE tax, but can include commissions, alimony and separate maintenance, and nontaxable combat pay ).
See this IRS link for Traditional IRA deduction limits when covered by a retirement plan at work.
https://www.irs.gov/Retirement-Plans/IRA-Deduction-Limits