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Due Date Calculator

The One Test. Two Lives. Due Date Calculator provides the estimated date of delivery and gestational age based on the date of a woman’s last period. After 8 weeks, the calculator also provides the estimated length and weight of the baby. Most importantly, this tool highlights the ideal time to test a pregnant woman for HIV and provides reminders that it is never too late to test for HIV.

How to Feature the Due Date Calculator Widget on Your Website

Copy this code to add the Due Date Calculator Widget to your website.

How to Use the Due Date Calculator Widget

  1. Click the “Calendar” icon to select the first date of your last menstrual cycle.
  2. Click the “Calculate” button to view estimated date of delivery and corresponding HIV testing recommendation based on trimester. To view an HIV testing recommendation for a different trimester, click the “First,” “Second,” or “Third” trimester tab.
  3. Click the “Resources” tab to access links to HIV testing, perinatal HIV treatment information, and gestational information on the One Test. Two Lives. website.
  4. Click the “Gestational Information” tab to get gestational information that corresponds to the estimated delivery date and trimester calculations.

How the Due Date Is Calculated

The Due Date Calculator provides an estimated date of delivery by adding 280 days to the first day of the last menstrual period.

  • First trimester is week 0 through week 13 and 6/7 (months 1–3).
  • Second trimester is week 14 and 0/7 through week 27 and 6/7 (months 4–6).
  • Third trimester is week 28 and 0/7 to the birth – typically week 40 (months 7–9).

CDC HIV Testing Recommendations During Pregnancy

Identifying new HIV cases is critical to stopping perinatal HIV transmission. For that reason, obstetric providers should test all pregnant patients for HIV, preferably in the first trimester. Studies show that pregnant women are more likely to get tested for HIV if their providers strongly recommend it.

CDC recommends that all pregnant women be screened for HIV as early as possible during each pregnancy.

Prenatal HIV screening benefits mom and baby.

Women living with HIV who take antiretroviral medication during pregnancy and are virally suppressed can reduce the risk of transmission to 1% or less.

First Trimester

The first trimester is the optimal time to test for HIV.

CDC, along with American College of Obstetricians and Gynecologists (ACOG) and American College of Nurse-Midwives (ACNM), recommends routine HIV testing as part of first-trimester prenatal screening tests for all pregnant women using an opt-out practice. Ideally, women should be screened for HIV at their initial prenatal care visit or as early in pregnancy as possible, using a combination HIV antigen and antibody assay.

Second Trimester

Clinicians should perform the HIV test as soon as possible when providing prenatal care, even if the first visit is at 13 weeks or later.

Women who decline HIV screening early in prenatal care should be encouraged to be screened at subsequent visits. Without treatment, babies born to mothers with HIV have a 22% chance of becoming infected with HIV.

Third Trimester

Although HIV treatment is most effective when it is initiated early in pregnancy, there are still benefits to the mother and her baby if diagnosed and treated later in pregnancy.

CDC recommends repeat testing in the third trimester for women in areas with high HIV incidence or prevalence and for women who meet one or more of the following criteria:

  • injection-drug users and their sex partners,
  • women who exchange sex for money or drugs,
  • women who are sex partners of HIV-infected persons, and
  • women who have had a new or more than one sex partner during their pregnancy.

Any woman with an undocumented HIV status at the time of labor should be screened with an expedited HIV test unless she declines. Treatment to prevent perinatal transmission can be started if there is a positive result from an HIV test during the intrapartum period.

Gestational Information

The chart below provides an estimate of length and weight of the baby based on the gestational age.

Gestational Age Length (U.S.) Weight (U.S.)
(crown to rump)
8 weeks 0.6 inch 0.04 ounce
9 weeks 0.9 inch 0.07 ounce
10 weeks 1.2 inch 0.14 ounce
11 weeks 1.6 inch 0.25 ounce
12 weeks 2.1 inches 0.5 ounce
13 weeks 2.9 inches 0.8 ounce
14 weeks 3.4 inches 1.5 ounces
15 weeks 4.0 inches 2.5 ounces
16 weeks 4.6 inches 3.5 ounces
17 weeks 5.0 inches 4.9 ounces
18 weeks 5.6 inches 6.7 ounces
19 weeks 6.0 inches 8.5 ounces
20 weeks 6.5 inches 10.6 ounces
(crown to heel)
20 weeks 10.1 inches 10.6 ounces
21 weeks 10.5 inches 12.7 ounces
22 weeks 10.9 inches 15.2 ounces
23 weeks 11.4 inches 1.1 pounds
24 weeks 11.8 inches 1.3 pounds
25 weeks 13.6 inches 1.5 pounds
26 weeks 14.0 inches 1.7 pounds
27 weeks 14.4 inches 1.9 pounds
28 weeks 14.8 inches 2.2 pounds
29 weeks 15.2 inches 2.5 pounds
30 weeks 15.7 inches 2.9 pounds
31 weeks 16.2 inches 3.3 pounds
32 weeks 16.7 inches 3.8 pounds
33 weeks 17.2 inches 4.2 pounds
34 weeks 17.7 inches 4.7 pounds
35 weeks 18.2 inches 5.3 pounds
36 weeks 18.7 inches 5.8 pounds
37 weeks 19.1 inches 6.3 pounds
38 weeks 19.6 inches 6.8 pounds
39 weeks 20.0 inches 7.3 pounds
40 weeks 20.2 inches 7.6 pounds
41 weeks 20.3 inches 7.9 pounds
42 weeks 20.3 inches 8.1 pounds

Please note: Due date calculations, as well as length and weight data, are only estimates.