đŸ‘ļ

Due Date Calculator

Calculate your estimated due date using LMP, conception date, or IVF embryo transfer date. View key pregnancy milestones.

Your Due Date

About the Due Date Calculator — Due Date Calculator Pregnancy

The Oneyfy due date calculator pregnancy tool supports three medically recognised methods for estimating your baby's expected delivery date: by Last Menstrual Period (LMP) using Naegele's Rule, by known Conception or Ovulation Date, and by IVF Embryo Transfer Date (for Day 3, Day 5, or Day 6 blastocysts). Beyond the estimated due date, the results panel shows your current gestational age, current trimester, days remaining, pregnancy progress percentage, and a complete key dates calendar covering all major milestones from the anatomy scan to post-term.

Pregnant people and their partners use a due date calculator pregnancy tool from the moment they receive a positive test. The estimated due date anchors every subsequent appointment, decision, and preparation milestone. Midwives and OB-GYNs use the same Naegele's Rule calculation that underlies this tool to establish the expected delivery window. IVF patients benefit from the dedicated IVF transfer mode because their conception date is precisely known — making the IVF calculation more accurate than LMP dating for that group.

How to Use the Due Date Calculator

  1. Select your calculation method using the tabs: By LMP (most common), By Conception, or By IVF.
  2. In By LMP mode: enter the First Day of Last Menstrual Period and, if your cycle differs from 28 days, enter your Average Cycle Length (accepted range: 21–45 days) for a more personalised estimate.
  3. In By Conception mode: enter the known or estimated Conception / Ovulation Date. The tool adds 266 days (38 weeks) to calculate the due date and derives the LMP equivalent as conception minus 14 days.
  4. In By IVF mode: enter the Embryo Transfer Date and select the Embryo Age at Transfer — Day 3 (cleavage stage), Day 5 (blastocyst, most common), or Day 6 (expanded blastocyst).
  5. Click Calculate Due Date — the results appear immediately showing your due date, gestational age, trimester, days remaining, and the full key dates calendar.

How the Three Calculation Methods Work

Each method uses a different starting point but ultimately derives the same equivalent LMP date for consistent gestational age tracking.

  • LMP Method (Naegele's Rule): Due Date = LMP + 280 days + (your cycle length − 28 days). For a standard 28-day cycle, this is simply LMP + 280 days. For a 30-day cycle, it's LMP + 282 days, accounting for the extra 2 days before ovulation typically occurs.
  • Conception Method: Due Date = Conception Date + 266 days. The equivalent LMP is calculated as Conception Date − 14 days, since ovulation (and conception) typically occurs 14 days after the LMP in a standard cycle.
  • IVF Method: Due Date = Transfer Date + (280 − 14 − embryo day at transfer). For a Day 5 blastocyst transfer: Transfer Date + 261 days. For Day 3: Transfer + 263 days. For Day 6: Transfer + 260 days. The gestational age at transfer is 14 days plus the embryo day.

Tips for Getting the Best Results

A few considerations help you get the most accurate estimate from each calculation method.

  • Use LMP only if your cycle is regular: Naegele's Rule assumes consistent cycle lengths. If your cycles vary significantly month to month, the LMP-based estimate may be off by a week or more. In that case, early ultrasound dating (crown-rump length at 7–13 weeks) is more reliable and your doctor may adjust your due date accordingly.
  • Adjust cycle length for precision: The cycle length field accepts values from 21 to 45 days. If you have a 35-day cycle and enter this value, the calculator adjusts the due date by +7 days compared to the default 28-day assumption — a clinically meaningful difference that changes your trimester boundaries and milestone dates.
  • IVF patients: use the embryo day selector carefully: Day 5 blastocyst transfers are the most common in modern IVF clinics. Day 3 transfers are rarer but still performed. Using the wrong embryo day shifts the due date by 2–3 days. Your IVF clinic documentation will specify the embryo age at transfer.
  • Remember: due dates are estimates: Only about 5% of babies are born on their exact due date. Most births occur in the two-week window between 38 and 40 weeks gestation. The calculator's result is an estimated due date, not a confirmed delivery date — your healthcare provider may adjust it based on ultrasound measurements.
  • Use the key dates calendar for appointment planning: The results panel shows dated milestones including the anatomy scan window (weeks 18–20), viability milestone (week 24), third trimester start (week 27), and early and full term dates. Use these to anticipate appointment scheduling with your midwife or OB-GYN.

Why Use a Due Date Calculator Online

A browser-based due date calculator runs instantly on any device with no app installation and no account creation. All calculations happen locally in your browser — your LMP date, conception date, and IVF transfer details are never transmitted to any server, which is important for medical privacy. The tool can be used offline once the page has loaded, making it accessible even in areas with unreliable connectivity.

Pregnant individuals benefit from immediate answers during the anxious early days after a positive test, before a first appointment is scheduled. Partners and family members use it to understand the timeline. IVF patients — who often know their embryo transfer date precisely — get more accurate estimates from the IVF mode than from general due date calculators that only offer LMP input. Healthcare students and trainees also find the explicit Naegele's Rule formulas useful for learning gestational age calculation methods.

Frequently Asked Questions about Due Date Calculator Pregnancy

First-trimester ultrasound dating based on crown-rump length measurement (performed at 7–13 weeks) is the most accurate method, with a margin of error of about 5–7 days. LMP dating is reliable when your LMP date is known and your cycles are regular (28 days). IVF dating is highly accurate because the exact conception date and embryo age are known — more accurate than LMP dating for IVF pregnancies specifically.
Full term is defined as 39–40 weeks of gestation. Early term is 37–38 weeks, late term is 41 weeks, and post-term is 42+ weeks. These designations were updated in 2013 by ACOG (American College of Obstetricians and Gynecologists) to distinguish outcomes more precisely, since babies born at 37 weeks have measurably different health outcomes than those born at 39–40 weeks despite both previously being called "full term."
In natural conception, ovulation and fertilisation occur approximately 14 days after the LMP, so gestational age is counted from LMP even though the embryo is 2 weeks younger. In IVF, the embryo age at transfer is precisely documented. The calculator adds 14 days to the embryo day to establish the gestational age at transfer (e.g., a Day 5 embryo has a gestational age of 2 weeks + 5 days at transfer), then calculates the equivalent LMP date and due date from there.
Gestational age is the age of a pregnancy counted in weeks from the first day of the last menstrual period — not from the date of conception. This convention means a pregnancy is already counted as "2 weeks old" at the moment of conception. A full-term pregnancy at 40 gestational weeks means the embryo is approximately 38 weeks old from fertilisation. All standard pregnancy milestones, trimester boundaries, and dating scans use gestational age.
Yes, completely free. No account, no sign-up, and no usage limits. All calculations run entirely in your browser — no dates or personal data are ever sent to any server. You can use it as many times as you like, and it works offline once the page has loaded, making it accessible even without a reliable internet connection during early pregnancy when you may be using it frequently.
The calculator uses the same date mathematics regardless of the number of babies, since the gestational age and nominal due date are calculated identically for singleton and multiple pregnancies from the LMP or transfer date. However, doctors typically manage twin and multiple pregnancies toward earlier delivery targets (37–38 weeks for dichorionic twins, 36 weeks for monochorionic), so your actual delivery planning timeline may differ from the 40-week due date this tool calculates.
If you're unsure of your exact LMP date, use the By Conception mode if you know approximately when you ovulated or conceived. Alternatively, an early ultrasound (ideally before 13 weeks) can establish the gestational age more reliably than an uncertain LMP date. Your healthcare provider will use the ultrasound measurement to set or confirm your due date if your LMP is uncertain.
Yes. The due date calculator works fully on mobile browsers including Safari on iOS and Chrome on Android. The date pickers use the device's native date input interface. All three calculation modes, the key dates calendar, and the progress bar are visible and functional on mobile screens. This makes it easy to check your pregnancy timeline from your phone during appointments or when sharing information with your partner.