There’s no arguing—medical screenings save lives.

Doctors say early detection could prevent nearly 100 percent of colon cancer cases, and for women ages 50 to 69, regular mammograms may lower the risk of breast cancer by up to 30 percent. But with so many tests out there, sometimes it’s hard to know which ones you really need.

Here’s a cheat sheet, based on federal health guidelines for women, for five essential tests and when you should have them—plus two you can often do without.

Tests You Must Have

1. Blood Pressure Screening

Tests for: Signs of heart disease, kidney failure, and stroke

When to get it: At least every one to two years beginning at age 18; once a year or more if you have hypertension

2. Mammogram

Tests for: Breast cancer

When to get it: Every one to two years, beginning at age 40. If you know you’re at higher risk, talk to your doctor about when you should have them.

3. Pap Smear

Tests for: Cervical cancer

When to get it: Every year if you’re under 30; every two to three years if you’re 30 or older and have had three normal Pap smears for three years in a row

4. Colonoscopy

Tests for: Colorectal cancer

When to get it: Every 10 years, beginning at age 50. If you have a family history of colorectal cancer, you should have a colonoscopy 10 years before your relative was diagnosed.

5. Skin Exam

Tests for: Signs of melanoma and other skin cancers

When to get it: After age 20, once a year by a doctor (as part of a full checkup), and monthly on your own.

Tests You Can Skip or Delay

1. Bone Density Test (DEXA Scan)

What it is: X-rays that measures the amount of calcium and other minerals in a bone

Why you might skip it: Doctors use bone density tests to see if you have osteoporosis. You can probably do without it if you’re under 65 and are not at high risk. After age 65, federal guidelines say you should get a bone density test at least once.

2. Full-Body CT Scan

What it is: Digital X-rays that take 3-D images of your upper body

Why you might skip it: Sometimes promoted as way to catch health problems before they start, full-body CT scans pose several problems themselves. Not only do they use very high levels of radiation, but the tests often give false results, or reveal scary abnormalities that often turn out to be harmless.