Spousal support (alimony) generally is deductible to the payer and taxable to the recipient in the year it was paid. (IRC 215, 71) Thus, if a late payment toward an arrearage would have been deductible in the first instance if paid on time, it remains deductible from the payer’s gross income and taxable to the recipient’s gross income in the year it is actually paid.
Talk to your accountant for more and updated information and for specific advice about your tax situation.