Due Date & Ovulation Calculator
Pregnancy Due Date & Ovulation Calculator: Estimate EDD and Fertile Window.
This fast and accurate calculator estimates the due date using established clinical methods such as Naegele’s rule (LMP + 280 days) and indicates likely ovulation and the fertile window to support conception planning.
Inputs support LMP-based dating, cycle-length adjustments, and IVF-specific transfer dating, alongside guidance on first‑trimester ultrasound accuracy for reconciling dates with clinical care.
Results display estimated due date, gestational age today, trimester markers, probable ovulation day, and the 6‑day fertile window when conception is most likely.
All outputs are informational only and not medical advice; clinical dating and care decisions should be made with a healthcare professional.
What this page offers
EDD estimation from LMP using the standard 280‑day convention, suitable for typical 28‑day cycles.
Cycle-aware adjustments to EDD when cycles are shorter or longer than 28 days by considering that ovulation occurs approximately 14 days before the next expected period.
IVF/FET due date support from embryo transfer date with day‑3/day‑5 adjustments based on fertilization‑to‑birth intervals.
Ovulation and fertile window estimates based on cycle length, cervical mucus and BBT context, and survival times for egg and sperm.
A concise, mobile-friendly experience sits above the fold to satisfy intent quickly, with deeper educational sections below to capture long‑tail queries and provide clarity.
How due date is calculated
The most common approach is Naegele’s rule: add 280 days (40 weeks) to the first day of the last menstrual period (LMP) to estimate the expected date of delivery (EDD).
This can also be expressed as adding 7 days to LMP, subtracting 3 months, and adding 1 year, which approximates 280 days from LMP.
In LaTeX form, the rule is EDD=LMP+280 days, assuming a 28‑day cycle with ovulation around day 14.
Pregnancy duration varies, and a small percentage deliver exactly on the due date; clinical follow‑up refines timing as pregnancy progresses.
For cycles not equal to 28 days, a practical adjustment is to shift EDD by the difference between actual cycle length and 28, because ovulation typically occurs about 14 days before the next period.
For example, a 35‑day cycle implies later ovulation than day 14, often pushing EDD later when calculated from LMP.
Ultrasound dating and accuracy
First‑trimester ultrasound, particularly crown‑rump length (CRL), is the single most accurate method to establish gestational age and may refine or replace LMP-based EDD when discrepancies exceed accepted thresholds.
Clinical protocols recommend considering pregnancies “suboptimally dated” if no confirmatory scan occurs by 22 weeks, prompting careful management and documentation.
When LMP and ultrasound dates differ, first‑trimester ultrasound generally provides a more reliable EDD, with guidance on when to “redate” based on measured differences and gestational age at the scan.
Accuracy tapers later in pregnancy; hence early ultrasound is preferred for definitive dating in clinical settings.
Ovulation and fertile window
The fertile window spans about six days—five days before ovulation plus the day of ovulation—reflecting sperm survival up to five days and an egg’s fertile lifespan of roughly 12–24 hours after release.
Likelihood of conception peaks during the two to three days before ovulation when viable sperm are present as the egg is released.
Signs and tools that help estimate ovulation include calendar tracking, cervical mucus changes, basal body temperature (BBT) shifts, and ovulation predictor kits detecting LH surges.
Typical cycles are often taught as 28 days, but healthy ranges can vary between roughly 21 and 35 days, influencing ovulation timing within the cycle.
IVF and assisted reproduction
For IVF or frozen embryo transfer (FET), the due date can be estimated from the embryo transfer date by accounting for embryo age, then adding the typical 266‑day interval from fertilization to birth.
A commonly used practical shortcut is adding 263 days after a day‑3 transfer or 261 days after a day‑5 blastocyst transfer, reflecting time already elapsed pre‑transfer.
Formally, EDD=Transfer Date+(266−d) days, where d is embryo age in days at transfer.
These IVF methods align with clinical practice for assisted reproduction timelines and produce due dates comparable to those derived from known conception.
How to use the calculator
Select LMP-based mode, IVF mode, or ovulation mode to match the intended task.
For LMP mode, enter the first day of the last period and cycle length to see EDD, gestational age today, and trimester milestones.
For IVF mode, enter transfer date and embryo day (3 or 5) to compute EDD and a reference early-scan window.
For ovulation mode, enter average cycle length to estimate ovulation day and the 6‑day fertile window.
Clear labels, accessible controls, and immediate results follow Google’s usability and quality guidance for task-oriented pages.
Key formulas and definitions
Naegele’s rule: EDD=LMP+280 days for a typical 28‑day cycle.
Ovulation anchor: ovulation is often approximated at Cycle Length−14 days before the next period, acknowledging individual variability.
IVF adjustment: EDD=Transfer Date+(266−d) days, where d is embryo age at transfer.
Fertile window: five days before ovulation through ovulation day due to sperm and egg viability windows.
These definitions underpin the calculator’s outputs and reflect mainstream clinical and patient-education resources.
Interpreting results
EDD is an estimate, not an appointment; most births occur within a multi-week window rather than exactly on the predicted day.
First‑trimester ultrasound may refine or revise EDD based on CRL and accepted clinical thresholds to reduce dating error.
Fertile window estimates are probabilistic and vary with cycle variability, stress, illness, and other factors; real-time signs and ovulation tests can improve precision.
IVF EDDs are anchored to known transfer timing, offering added precision versus uncertain natural conception dates.
Irregular cycles and adjustments
When cycles are irregular, LMP-based estimation may be less accurate, and an early ultrasound becomes more valuable for establishing gestational age.
Cycle-aware tools that consider ovulation variability and symptom tracking can improve fertile-window estimation for conception planning.
For markedly irregular cycles, follow-up with a clinician for individualized dating and care planning is recommended.
Healthcare guidance underscores the importance of the first-trimester scan when LMP is uncertain or cycle length is atypical.
Medical context and safety
EDD calculators are informational tools that should complement—not replace—clinical assessment, prenatal care, and ultrasound-based dating where indicated.
Always seek clinician guidance on medications, risk factors, or symptoms during pregnancy rather than relying solely on calculators.
Estimate Due Date from LMP or IVF transfer in seconds and see the likely ovulation day with a 6‑day fertile window, adjusted for cycle length where applicable.
Results include EDD, gestational age today, trimester markers, fertile window, and IVF day‑3/day‑5 transfer logic to align with clinical timelines.
What the results mean
Due date (EDD): a 40‑week estimate from LMP or IVF timing; final clinical dating may be refined by early ultrasound.
Gestational age today: time elapsed since pregnancy dating origin, presented in weeks and days for clarity.
Fertile window: the six days before and including ovulation when conception is most likely based on sperm and egg lifespans.
Special cases
IVF/FET: apply day‑3/day‑5 adjustments from transfer date per assisted reproduction convention.
Irregular cycles: treat LMP-based estimates cautiously and consider early ultrasound for definitive dating.
Practical tips
Use cervical mucus observations, BBT, or LH kits to better time the fertile window if cycles vary.
Schedule routine prenatal care, and discuss ultrasound timing and any re-dating questions with the care team.
FAQs
How is the due date calculated from LMP?
Most calculators add 280 days to the first day of the last menstrual period for an estimated 40‑week EDD under Naegele’s rule.
What if cycles are longer or shorter than 28 days?
Because ovulation tends to occur about 14 days before the next period, longer cycles often shift EDD later and shorter cycles may shift EDD earlier.
Is ultrasound more accurate than LMP?
First‑trimester ultrasound (CRL) is generally more accurate and may be used to revise EDD if the discrepancy with LMP exceeds clinical thresholds.
How does IVF change due date calculation?
IVF EDD is based on transfer date and embryo age, commonly calculated as transfer date plus 263 days for day‑3 embryos or 261 days for day‑5 embryos.
What is the fertile window?
The fertile window spans about six days—the five days before ovulation plus ovulation day—reflecting sperm viability up to five days and egg viability up to 24 hours.
Are these results medical advice?
No, all outputs are informational and do not replace clinical guidance; consult a clinician for personalized care and dating decisions.
Why do due dates change after a scan?
Early ultrasound can yield a more accurate gestational age than LMP, prompting clinicians to “redate” when differences exceed accepted thresholds.