Pregnancy Calculator

A pregnancy calculator estimates your due date, current pregnancy week, and baby development stage based on key dates you provide. Whether you are tracking your first pregnancy or planning your third, this tool delivers instant answers. Enter your last menstrual period (LMP), conception date, or ultrasound data to get started. According to the World Health Organization (WHO), most full-term pregnancies last between 37 and 42 weeks. The standard duration is 40 weeks, counted from the first day of the last menstrual period.

What Is a Pregnancy Calculator?

A pregnancy calculator is a digital tool that estimates how far along you are, your estimated due date (EDD), and your baby's current development milestone. It works by calculating 280 days from the first day of your last menstrual period. Other inputs include a conception date or IVF embryo transfer date. DigiCalc's pregnancy calculator supports three methods: LMP, conception date, and ultrasound gestational age, covering the full range of how pregnancies are dated in clinical practice.

Pregnancy Due Date Calculator: How Your Due Date Is Estimated

The standard formula is Naegele's Rule. It adds 280 days (40 weeks) to the first day of your last menstrual period. The formula is:

Estimated Due Date = LMP Date + 280 days

This calculation assumes a 28-day menstrual cycle with ovulation occurring on day 14. As an example: if your last period started on January 1, your estimated due date would be October 8 of the same year.

Only about 4% of babies are born on their exact estimated due date. The CDC confirms that most births fall within two weeks before or after the estimated date. Only 4% of babies arrive exactly on their due date. A pregnancy due date calculator provides a planning target, not a guaranteed delivery date.

How to Use This Pregnancy Calculator

1. Select your calculation method: Last Menstrual Period, Conception Date, or Ultrasound.
2. Enter the relevant date in the input field (LMP date, conception date, or ultrasound date plus gestational age at scan).
3. If using LMP, select your average cycle length (21 to 35 days) to improve accuracy.
4. Click "Calculate Due Date" to see your estimated due date, current week, trimester, and baby's development stage.

LMP Calculator: Calculating Your Due Date from Last Menstrual Period

The LMP calculator is the most widely used method for estimating a due date. Enter the first day of your last menstrual period and your average cycle length. The calculator adds 280 days to your LMP date. It adjusts for cycles shorter or longer than 28 days. This is the standard method used by OBGYNs and midwives globally. It works best when you have regular menstrual cycles and know the exact start date of your last period.

The last menstrual period calculator assumes ovulation occurs 14 days into your cycle. For a 30-day cycle, ovulation is estimated at day 16. This shifts your due date two days later than a standard 28-day calculation. The pregnancy week calculator by lmp is the foundation of all date-based pregnancy tracking. It remains the clinical default even when ultrasound confirms a slightly different gestational age. Many users ask: how many weeks am I pregnant from my last period? Enter your LMP date into the calculator above, and your current gestational age in weeks and days appears immediately.

IVF Due Date Calculator: Due Dates for IVF Pregnancies

The IVF due date calculator works differently from LMP-based calculations because the conception date is known precisely. For a Day 5 blastocyst transfer, the due date is calculated as the transfer date plus 261 days. For a Day 3 embryo transfer, it is the transfer date plus 263 days.

IVF Day 5 Transfer: Transfer Date + 261 days = Estimated Due Date

IVF Day 3 Transfer: Transfer Date + 263 days = Estimated Due Date

IVF conception timing is documented precisely. Because of this, the gestational age calculator for IVF pregnancies carries less uncertainty than LMP-based estimates. The NIH notes that IVF pregnancies benefit from precise embryo dating. This makes the estimate more reliable than in natural conceptions where ovulation timing is uncertain.

For IVF pregnancies, select the Conception Date method. Enter a date 14 days before your transfer date for Day 5, or 12 days before for Day 3. This aligns the tool with clinical IVF dating conventions.

Pregnancy Week Calculator: Understanding Your Current Stage

The pregnancy week calculator tells you exactly how many weeks and days pregnant you are as of today. It counts the days elapsed since your LMP or estimated conception date and converts that number into weeks and days. Knowing your current week helps you prepare for prenatal appointments, understand which trimester you are in, and track your baby's development milestones.

Using a pregnancy calculator week by week helps you stay informed at every stage. At week 8, the baby is the size of a raspberry (about 1.6 cm). By week 20, the baby reaches the size of a banana (about 16.4 cm). At full term (week 40), the baby is roughly the size of a small watermelon, averaging 50 cm in length and 3,200 grams in weight.

Understanding Your Pregnancy Calculator Results

Your pregnancy calculator results include four key pieces of information:

• Estimated Due Date (EDD): The projected birth date, 280 days from LMP. Treat this as a target window of plus or minus two weeks, not a fixed date.
• Current Gestational Age: How far along you are in weeks and days. Gestational age counts from LMP, not from conception. That is why it starts at "week 1" two weeks before conception occurred.
• Current Trimester: First (weeks 1-13), second (weeks 14-26), or third (weeks 27-40), based on your current gestational week.
• Baby Development Stage: A size comparison and developmental milestone corresponding to your current week, drawn from published fetal growth reference data.

Gestational age and fetal age are not the same. Gestational age counts from LMP. Fetal age counts from conception and is typically two weeks less. When your doctor says "12 weeks pregnant," they mean gestational age. The baby has only existed for about 10 weeks since fertilization.

Pregnancy Calculator Examples

Example 1: LMP Method (regular 28-day cycle)
Last menstrual period: March 1. Average cycle length: 28 days.
Estimated due date: March 1 + 280 days = December 6.
If today is July 15, the pregnancy is at 19 weeks and 2 days. Current stage: Second Trimester. Baby size: approximately the size of a mango at 15 cm.

Example 2: Conception Date Method
Known conception date: March 15. DigiCalc's conception date calculator subtracts 14 days to determine the LMP equivalent (March 1), then adds 280 days.
Estimated due date based on conception: December 6. This confirms the same result as Example 1, showing how both methods align when the 28-day cycle assumption holds.

Example 3: IVF Blastocyst (Day 5) Transfer
Transfer date: April 10.
Estimated due date: April 10 + 261 days = December 27.
At 12 weeks gestational age, the baby in this IVF pregnancy has completed organogenesis (all major organs are present) and weighs approximately 14 grams.

Pregnancy Month Calculator: Converting Weeks to Months

Many expectant parents want to know their pregnancy in months, not just weeks. The pregnancy month calculator by week divides gestational age by 4.33 (the average number of weeks per calendar month) to give an approximate month figure. However, this conversion is approximate because pregnancy months in clinical use are counted in 4-week blocks, not calendar months.

How Many Weeks Pregnant Am I Based on My Due Date?

To find how many weeks pregnant you are from a due date, subtract the remaining days from 280. For example: if 127 days remain, you are 153 days pregnant. That equals 21 weeks and 6 days. This reverse due date calculator approach works whenever you know your due date but not your LMP.

Baby Size by Week: Fetal Development Chart

These measurements are population averages based on published fetal growth reference charts. Individual babies vary significantly in size. A measurement above or below average does not necessarily indicate a health concern. Your healthcare provider will assess growth through ultrasound and fundal height during prenatal visits.

Limitations of Pregnancy Due Date Calculations

Pregnancy calculators provide estimates based on population averages, not individual measurements. Several factors reduce accuracy:

• Irregular cycles: The LMP method assumes a 28-day cycle. Women with irregular periods, PCOS, or hormonal conditions may ovulate later than day 14, making the LMP estimate less accurate.
• Uncertain LMP date: If the exact start date of the last period is not known, the estimate carries greater uncertainty.
• Biological variation in pregnancy length: Full-term pregnancies naturally range from 37 to 42 weeks. A due date is the midpoint of a natural 5-week delivery window.
• Multiple pregnancies: Twins, triplets, and higher-order multiples typically deliver before 40 weeks. Standard due date formulas are not designed for multiple gestations.
• Implantation timing: Fertilization and implantation can occur at different points in the cycle, shifting the true gestational age away from LMP-based estimates.

For the most accurate pregnancy dating, an early ultrasound between 8 and 13 weeks is the clinical gold standard. This scan uses fetal crown-rump length (CRL) to determine gestational age with greater precision than any date-based method.

Prenatal Care Tips by Trimester

First Trimester (Weeks 1-13):

• Begin prenatal vitamins with 400-800 mcg of folic acid as soon as pregnancy is confirmed. The CDC recommends folic acid to reduce the risk of neural tube defects such as spina bifida by up to 70%.
• Book your first prenatal appointment early. It typically includes blood tests, blood pressure assessment, urine screening, and an initial ultrasound.
• Avoid alcohol, tobacco, and high-mercury fish (shark, swordfish, king mackerel) throughout the entire pregnancy.
• Expect fatigue, nausea, and breast tenderness. These are normal responses to rising hCG and progesterone levels in early pregnancy.

Second Trimester (Weeks 14-26):

• Schedule your anatomy scan at 18-20 weeks. This detailed ultrasound checks baby's organ development, growth measurements, and placenta position.
• Begin tracking fetal movement after week 20. Most women feel the first kicks (called quickening) between weeks 16 and 25.
• Maintain moderate exercise such as walking, swimming, or prenatal yoga, with your provider's approval.
• Monitor weight gain. The WHO recommends 11-16 kg of total weight gain during pregnancy for women with a healthy pre-pregnancy BMI.

Third Trimester (Weeks 27-40):

• Increase prenatal appointment frequency. Most providers schedule visits every two weeks after week 28, then weekly from week 36 onward.
• Complete a birth plan and discuss it with your healthcare team before week 36.
• Learn the signs of labor: regular contractions, rupture of membranes, or bloody show. Contact your provider immediately if these occur before week 37.
• Use DigiCalc's pregnancy weight gain calculator to monitor healthy weight gain week by week through the final trimester.

For a complete pregnancy toolkit, DigiCalc offers an ovulation calculator to track your fertile window. A conception calculator is also available to estimate when conception occurred. All tools are available in the pregnancy calculators collection.