A big healthcare decision for military veterans comes with turning 65, and that is whether to enroll in Medicare.

People who have TRICARE and plan to enroll in TRICARE for Life - a program managed by the Department of Defense - are generally out of options. It is only available if they have Medicare Part A (hospital coverage) and Part B (outpatient care coverage). However, the decision might be more challenging for veterans who rely on the VA for their benefits.

Each year, the VA health system treats 9 million veterans across the country at its 1,293 facilities, including 171 hospital centers and over 1,112 outpatient sites. Outside of those places, however, it usually does not cover services.

Health care providers often accept Medicare. VA itself recommends signing up as soon as eligible for VA benefits since this varies from person to person based on wellness and military service history. Enrollment begins three months before your 65th birthday and concludes three months after your 65th birthday.

Although some veterans use VA health care, they do so to obtain their medicine from non-VA doctors and fill their prescriptions at their local pharmacy instead of using the VA mail-order service, which processes roughly 80% of outpatient prescriptions.

Meanwhile, some veterans with VA health care who enroll in Medicare choose a Medigap policy rather than an Advantage Plan (you cannot have both).

Upon enrolling for Medicare, you begin the "guaranteed-issue" period. This sort of supplemental insurance can cover some deductibles, copays and coinsurance connected with Medicare. However, unless you live in a state with different standards, you usually only have six months to get Medigap coverage before an insurance company looks over your medical records and decides whether or not to insure you.

After that window has passed, you may need to undergo medical underwriting. Depending on your health, the Medigap insurer may raise your premiums or refuse to cover you at all.