Pregnancy Calculator

Pregnancy Calculator: Find Your Due Date and Gestational Age in Seconds

Pregnancy calculator is a free digital tool that estimates your expected due date (EDD), current gestational week, days remaining until birth, and trimester — using whichever data you have on hand. Formula: add 280 days to the first day of your last menstrual period (LMP), then adjust for cycle length deviations. This principle, known as Naegele's rule, is the foundation of due-date estimation in obstetric practice across the United States, the United Kingdom, and worldwide.

What Does the Pregnancy Calculator Do?

The tool combines four clinically recognised estimation methods under one interface: Last Menstrual Period (LMP), Conception Date, Ultrasound Date, and IVF Embryo Transfer. Beyond the due date, it displays the baby's approximate size compared to a fruit or vegetable based on peer-reviewed fetal growth charts, lists 14 key pregnancy milestones (heartbeat detection, anatomy scan, viability week, and more), and — if you provide your pre-pregnancy weight and height — calculates gestational weight gain guidance aligned with ACOG and WHO recommendations. In the US, many expectant mothers open a calculator like this the same week they get a positive test result, long before their first OB appointment at week 8 or 10.

Calculation Methods and Formulas

Each method requires different input data. Choose the one that best matches what you currently know, and always verify the result with your healthcare provider.

Method	Required Input	Formula	Best Used When
Last Menstrual Period (LMP)	LMP date, cycle length	LMP + 280 days ± cycle adjustment	Cycles are regular and dates are known
Conception Date	Conception date	Conception + 266 days	Ovulation date is known
Ultrasound	Scan date, weeks + days	Scan date − gestational days + 280	Irregular cycles or late prenatal care
IVF Transfer	Transfer date, embryo type	Day 5: +259 days / Day 3: +261 days	Assisted reproduction pregnancies

Example 1 — LMP: LMP is January 5, 2026 with a standard 28-day cycle. EDD = January 5 + 280 days = October 12, 2026.
Example 2 — Ultrasound: Scan performed February 1, 2026 showing 10 weeks 3 days. Back-calculated LMP ≈ November 23, 2025; EDD = August 29, 2026.
Example 3 — IVF: Day-5 blastocyst transfer on February 15, 2026. EDD = February 15 + 259 days = October 31, 2026.

Real-World Scenarios

First-Time Moms Before the First OB Visit

In the US, most OB-GYN practices schedule the first prenatal appointment between 8 and 10 weeks. That leaves several weeks after a positive home pregnancy test with no official confirmation of the due date. Using the LMP method, a first-time mother who got a positive result on January 20 can immediately estimate she is around 4 weeks pregnant — giving her time to research prenatal vitamins, arrange insurance coverage under her employer's health plan, and plan a disclosure timeline for her workplace.

IVF Patients at Fertility Clinics

Assisted reproduction pregnancies in the US now account for roughly 2% of all births annually. Patients who have completed a frozen embryo transfer often know their exact transfer date and embryo grade. By selecting the IVF method and specifying Day 5 or Day 3, they receive an immediate due date estimate — useful for planning maternity leave under the Family and Medical Leave Act (FMLA) and for early communication with their HR department.

Managing Weight Gain Guidelines

The American College of Obstetricians and Gynecologists (ACOG) recommends weight gain of 11.5–16 kg for women with a normal pre-pregnancy BMI. By entering pre-pregnancy weight and height into this tool, expectant mothers see an instant personalised target range — a helpful reference to discuss with their midwife or OB at each visit.

Who Can Use This Tool?

Expectant mothers — Anyone who has just discovered they are pregnant and wants to know their due date
Couples planning maternity and paternity leave — Mapping leave windows under FMLA or employer policies
IVF patients — Calculating EDD immediately after embryo transfer
Midwives and doulas — Quickly estimating gestational age for client intake
Prenatal educators — Demonstrating milestone timelines in childbirth classes
Family members — Grandparents-to-be and siblings counting down to the birth
Pregnancy bloggers and content creators — Generating week-by-week development content
Nursing and midwifery students — Practising obstetric dating formulas

Final Notes and Next Steps

This pregnancy calculator gives you a reliable, evidence-based starting point for understanding your gestational timeline. Whether you're using LMP, a recent ultrasound report, or an IVF transfer date, the tool applies the same formulas used in clinical obstetrics. Please remember: this tool provides estimates only and is not a substitute for professional medical advice, diagnosis, or treatment. Always confirm your due date and pregnancy milestones with a qualified OB-GYN or certified nurse midwife. For authoritative guidance, refer to the American College of Obstetricians and Gynecologists (ACOG) at acog.org.

Key Takeaways:
All results are estimates; they do not constitute medical advice and must be verified by a licensed healthcare provider.
First-trimester ultrasound (8–12 weeks) is the most accurate method for establishing gestational age.
Enter your actual cycle length if it differs from 28 days to improve due date accuracy.
IVF patients must select the correct embryo transfer day (Day 3 or Day 5) for a precise estimate.
Use this tool as a planning aid, then follow up with your prenatal care team for all clinical decisions.

How to Use

Choose your calculation method

Select the method that matches your available information: Last Menstrual Period, Conception Date, Ultrasound Date, or IVF Transfer.

Enter the required date and details

Fill in the relevant date field and any additional information, such as cycle length for the LMP method or gestational weeks and days for the ultrasound method.

Add optional weight and height data

If you want a gestational weight gain recommendation, enter your pre-pregnancy weight in kg and your height in cm — both fields are optional.

Review your personalised results

The calculator instantly displays your estimated due date, current week, trimester, baby size comparison, days remaining, and upcoming pregnancy milestones.

Share results with your healthcare provider

Bring the estimated due date and milestone timeline to your next prenatal appointment so your OB-GYN or midwife can confirm the figures and adjust your care plan if needed.

Frequently Asked Questions

The most common method is Naegele's rule: add 280 days (40 weeks) to the first day of your last menstrual period (LMP), then adjust for cycle length if it differs from 28 days. If you use the ultrasound method, the tool back-calculates an estimated LMP from your scan date and gestational age, then adds 280 days. For IVF, the formula uses your transfer date plus a fixed offset based on embryo age (259 days for blastocyst, 261 days for Day 3). Only your OB-GYN can confirm your official due date.

LMP-based estimates carry a typical margin of ±1–2 weeks, since ovulation timing varies even in regular cycles. A first-trimester ultrasound can narrow this to roughly ±3–5 days and is considered the gold standard for gestational dating before 14 weeks. This tool applies the correct clinical formulas, but individual pregnancies vary. Please confirm your due date with your healthcare provider at your first prenatal appointment.

Select IVF Transfer from the method menu, enter your embryo transfer date, and choose Day 5 (blastocyst) or Day 3 embryo. The tool adds 259 days for a Day-5 transfer and 261 days for a Day-3 transfer. This difference exists because the embryo is already 5 or 3 days old at the time of transfer. Always cross-check this estimate with your reproductive endocrinologist's records.

Enter your actual cycle length in the cycle length field; the tool accepts values between 20 and 45 days. The calculator automatically adds or subtracts the difference from 28 days when computing your EDD. For example, a 35-day cycle shifts the due date 7 days later compared to a standard 28-day cycle. This adjustment is a standard extension of Naegele's rule used in clinical practice.

Each week, the tool shows your baby's estimated length and weight alongside a fruit or vegetable of a comparable size, based on published fetal growth reference charts. At 20 weeks, for example, a baby is approximately the size of a banana — about 162 mm long and 300 g. This is a widely used patient education tool to make fetal development tangible; actual size can only be measured by ultrasound.

Enter your pre-pregnancy weight (kg) and height (cm), and the tool calculates your pre-pregnancy BMI. It then displays the recommended gestational weight gain range according to ACOG and WHO guidelines: Underweight (BMI < 18.5): 12.5–18 kg; Normal (18.5–24.9): 11.5–16 kg; Overweight (25–29.9): 7–11.5 kg; Obese (≥ 30): 5–9 kg. These are general guidelines; your personal weight management plan should be supervised by your OB-GYN or a registered dietitian.

Yes, the tool is completely free and requires no account or registration. The calculations are performed instantly in your browser, and no personal health data is stored on our servers. You can use it as many times as you like throughout your pregnancy.

Absolutely. Enter the date on which the ultrasound was performed — not today's date — along with the gestational age reported on that scan. The tool will back-calculate from that historical scan date, giving you an accurate EDD regardless of how long ago the scan took place.

Pregnancy Calculator

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