First, it is important to understand that everything of value that is provided to you by your employer in return for your services is considered taxable income to you, unless it falls under one of the protected categories of fringe benefits.
Health insurance benefits for yourself, your spouse, and your dependents are in the protected category of non-taxable benefits. Your share of the premium is deducted from your paycheck on a pre-tax basis, and your employer is allowed to pay part of your premium without considering it part of your taxable income.
For a non-dependent DP covered by your insurance, if your employer requires you to pay part of the premium, that is deducted from your paycheck after tax, not before tax. And if your employer pays part of the premium for you, that must be added to your wages. It would be included in box 1 of your W-2 at the end of the year and is subject to income tax, Social Security tax and Medicare tax withholding, as if you had received the same amount as a raise.
It sounds as though the total cost of your partner’s insurance coverage is $523 per month. The $250 paid by your employer is the imputed income, and the $273 that you will be paying is your after-tax share of the premium.
