MFJ both owe back taxes

[kmarteny]

If my husband and I file jointly and both owe from previous years when not married, how is the refund split between our individual balances?

[xmasbaby0]

If you both owe back taxes, the refund on your joint return will be seized up to the amount owed.    The IRS will send you a letter a few weeks later that explains why the refund was offset.   You can also check your own online IRS accounts afterward to see your remaining individual balances owed.

https://www.irs.gov/payments/your-online-account

[kmarteny]

I guess my question is will the refund amount from my income go towards my debt and same for his? 

[xmasbaby0]

@kmarteny We cannot predict how much of the refund is "yours" and how much is your spouse's, nor can we predict how much of the seized refund will be attributed to your debt or to your spouse's debt.  When you file a joint tax return, there is no "his and hers" to the refund.   It is a joint refund in both names.   That should be explained in the letter the IRS will mail to you, and will be shown in your online accounts with the IRS.