Pregnancy Calculator

Pregnancy Term & Due Date

A typical pregnancy lasts about 40 weeks, or 280 days, counted from the first day of the last menstrual period (LMP) rather than from conception. The convention exists because most people know when their period began but not the day they ovulated, which usually falls about two weeks later. As a result, conception happens at roughly two weeks of pregnancy by this count.

Babies born from 37 weeks 0 days to 38 weeks 6 days are early term, from 39 weeks 0 days to 40 weeks 6 days full term, at 41 weeks late term, and at 42 weeks or later post term; birth before 37 weeks is preterm. The due date marks 40 weeks, but only a small share of babies arrive on that exact day.

The calculator offers five ways to date a pregnancy. From the last period it adds 280 days, adjusted for cycle length; from a conception date it adds 266 days; from an IVF transfer it uses the transfer date and the embryo's age. An early ultrasound measuring the embryo is the most accurate method, and providers often adjust the due date to match it.

Due date = first day of last period + 280 days (40 weeks)

This is Naegele's rule, adjusted for cycle length: each day your cycle is longer than 28 days moves the due date one day later. From a conception date, add 266 days; from an IVF transfer, add 266 days minus the embryo's age; from an ultrasound, count forward from the gestational age it measured.

Pregnancy Detection

Once a fertilized egg implants in the uterus, about 6 to 12 days after ovulation, the developing placenta begins releasing the hormone hCG, which pregnancy tests detect. Home urine tests are most reliable from the day of a missed period, and testing with first-morning urine helps. A negative result before then may simply be too early, so repeat it a few days later. Blood tests at a clinic detect smaller amounts and can measure the level. Early signs such as a missed period, breast tenderness, nausea, fatigue and frequent urination vary widely from person to person.

Pregnancy Management

Good prenatal care is one of the most effective ways to support a healthy pregnancy. Book a first appointment soon after a positive test, typically around eight weeks. That visit confirms the pregnancy and due date, reviews your medical history and medications, and sets up a schedule of checkups: usually every four weeks until about 28 weeks, every two weeks until 36 weeks, and weekly until delivery.

Routine care includes blood and urine tests, blood pressure checks, optional genetic screening in the first and second trimesters, a detailed anatomy ultrasound at around 18 to 22 weeks, screening for gestational diabetes between 24 and 28 weeks and a group B strep test at 36 to 37 weeks. Recommended vaccines, such as the flu shot and Tdap, protect both parent and baby.

Day-to-day choices matter as well. The following habits are widely recommended by obstetric and public health organizations:

• Take a daily prenatal vitamin with at least 400 micrograms of folic acid, ideally starting a month or more before conception, to reduce the risk of neural tube defects.
• Avoid alcohol, tobacco, vaping and recreational drugs entirely; no amount of alcohol is known to be safe in pregnancy.
• Limit caffeine to about 200 milligrams a day, roughly one 12-ounce cup of coffee.
• Skip foods with a higher risk of foodborne illness, such as unpasteurized dairy and juice, raw or undercooked meat, eggs and seafood, and deli meats unless heated, and choose fish low in mercury.
• Stay active with about 150 minutes of moderate exercise a week, such as walking or swimming, unless your provider advises otherwise.
• Gain weight within the range recommended for your starting BMI; the pregnancy weight gain calculator shows the target for each trimester.

Check with your provider before starting or stopping any medication, including over-the-counter drugs and supplements. Rest, a balanced diet with plenty of fruit, vegetables, whole grains and protein, and enough water help with common discomforts like fatigue, constipation and swelling.

Seek care promptly for vaginal bleeding, leaking fluid, severe abdominal pain, a severe headache or vision changes, fever, sudden swelling of the face or hands, regular contractions before 37 weeks, or a noticeable drop in the baby's movements in the third trimester. These can signal problems that need attention right away.

Frequently asked questions

Sources

• ACOG – Methods for Estimating the Due Date
• ACOG – Definition of Term Pregnancy
• CDC – Folic Acid