Medicare isn't enough for retirees - here's how much extra coverage costs in every state, ranked

• Medicare doesn't cover every health cost - retirees need to save for Medigap plans, extra health insurance policies that help pay for some of the health care costs traditional Medicare doesn't cover.
• HealthView Services provided Business Insider with average annual cost projections for Medigap Plan F, the most popular level of Medigap coverage, in every state.
• Medigap plans are most affordable in Hawaii and most expensive in Washington, DC.

Saving for retirement seems to be never ending.

It's twice as expensive to retire today as it was 25 years ago, writes James Moore in MarketWatch. And according to one financial planner, millennials need more than $1 million saved by the time they retire.

One cost often overlooked when it comes to saving for retirement? Medigap plans. Because Medicare doesn't cover everything.

Medigap plans are extra health insurance policies sold by private companies that help pay for some of the health care costs traditional Medicare doesn't cover, such as copayments, coinsurance, and deductibles. Some Medigap plans even cover services, such as medical care when traveling outside the US.

Retirees must have Medicare Part A and Medicare Part B to have a Medigap plan.

HealthView Services provided Business Insider with the average annual cost projections for Medigap Plan F, the most popular level of Medigap coverage, across every state.

The national average cost for Medigap Plan F is $1,712 annually, which is around $143 a month.

Medigap Plan F is the most affordable in Hawaii, with an average annual projected cost of just $1,310 a year, or around $109 a month. In Massachusetts, it's much higher: The average annual projected cost of Medigap Plan F is $1,947, which is equivalent to roughly $162 a month.

Scroll through below to see how much Medigap Plan F costs in every state, plus Washington, DC.