Saving for retirement might be easier if you know how much money you'll actually need.

It's a tough number to nail down, but a new report estimates how much you'll spend on what's likely to be your biggest expense: health care.

A couple retiring this year will need $260,000 to cover health care costs in retirement, according to Fidelity.

It's a ballpark number, but it's helpful to keep it in mind as you plan out your retirement.

The estimate applies to those with traditional Medicare insurance coverage and considers premiums, co-payments, deductibles, and out-of-pocket drug costs. It assumes that both spouses are 65 years old.