Pregnancy Calculator
Calculate your pregnancy due date, current week, and trimester from LMP.
Written by Golam Rabbani, Founder & Lead Engineer — Last updated 2026-05-01
How to use this pregnancy calculator
- Choose how to date the pregnancy: last menstrual period (LMP), conception date, ultrasound scan, IVF transfer (3- or 5-day), or a known due date (reverse).
- Enter the relevant date. For the LMP method, optionally set your average cycle length (22–44 days) to cycle-correct the due date; results update live as you type.
- Read the estimated due date, trimester, a percent-complete progress bar, current gestational age (weeks + days and months), days remaining, and the estimated conception date.
- Open the week-by-week schedule (1–40) for trimester-banded date ranges and milestones, or use “Check gestational age on a date” to see how far along you are on any day.
- Use Copy for a text summary, or “Add milestones to calendar (.ics)” to import the milestones into your calendar app; Reset clears everything.
About this pregnancy calculator
The pregnancy calculator takes the first day of your last menstrual period and returns your estimated due date, current gestational week, trimester, days remaining, and a key-milestones timeline — all in one screen.
The default method is Naegele's rule, the standard obstetric formula: due date = LMP + 280 days (40 weeks). Gestational age is then the number of days elapsed since the LMP divided into whole weeks and remaining days. The estimated conception date is placed about 14 days after the LMP, matching average ovulation in a 28-day cycle. Trimester boundaries follow common convention: weeks 1–12 are the first trimester, weeks 13–27 the second, and week 28 onward the third. This approach aligns with guidance from the American College of Obstetricians and Gynecologists (ACOG), which recommends confirming dates with an early ultrasound. This is an estimate for general information and is not a substitute for advice from a qualified clinician.
Because a 280-day count assumes a 28-day cycle with ovulation on day 14, the tool also lets you cycle-correct: the corrected LMP is LMP + (cycle − 28), so a 35-day cycle pushes the due date roughly a week later. Beyond LMP, you can date from a conception date (EDD = conception + 266 days), an ultrasound gestational age on the scan date, an IVF transfer (5-day blastocyst: transfer + 261 days; 3-day embryo: transfer + 263 days), or work backward from a known due date to estimate LMP and conception. Whichever method you pick, the tool reports the same set of results: due date, progress, gestational age, conception date, dated milestones, and a week-by-week schedule.
For example, an LMP of January 1, 2026 with a 28-day cycle gives a due date of October 8, 2026 and an estimated conception of January 15, 2026; switching to a 35-day cycle moves the due date to October 15, 2026. Parents-to-be, people tracking a cycle, and anyone preparing for an appointment will find this useful. This calculator is for general educational purposes only and is not medical advice — consult a licensed healthcare professional for personal guidance.
FAQ
- How does the pregnancy calculator estimate my due date?
- It applies Naegele's rule: your due date is 280 days (40 weeks) after the first day of your last menstrual period. This is the same baseline formula used in standard obstetric practice, though your care provider may adjust it based on an ultrasound dating scan.
- What formula does the tool use to calculate gestational age?
- Gestational age is the number of days elapsed since your LMP, divided into complete weeks and leftover days. So if 73 days have passed, the tool shows Week 10 + 3 days.
- How accurate is the estimated due date?
- The estimate is based on a typical 28-day cycle with ovulation at day 14. Cycle length, irregular periods, and other factors mean natural variation is normal — only about 5% of babies arrive on their exact due date. Always confirm dating with your healthcare provider.
- Can I use my cycle length, conception date, ultrasound, or IVF transfer date?
- Yes. The “Calculate based on” selector supports LMP (with an optional 22–44 day cycle-length correction), conception date, an ultrasound gestational age, and IVF 3-day or 5-day transfer dates. You can also enter a known due date to work backward to your estimated LMP and conception date. All methods produce the same set of results.
- How does cycle-length correction change my due date?
- The standard 280-day count assumes a 28-day cycle. For other cycle lengths the tool uses a corrected LMP of LMP + (cycle − 28) before adding 280 days. So a 35-day cycle adds about 7 days to the due date, and a 21-day cycle subtracts about 7 — a meaningful difference the basic LMP-only method misses.
- What happens if I enter a future LMP date?
- The date input is capped at today. If a future date is submitted, the tool shows an error and asks you to enter a valid past or current date.
- Does the pregnancy calculator store any of my data?
- No. The pregnancy calculator runs entirely in your browser. No dates or results are sent to a server, logged, or retained after you close the page.
- Is the pregnancy calculator free?
- Yes. It is completely free to use with no account, no signup, and no usage limit.