Weights and lengths are population averages. Growth is assessed by Z-score / percentile using the Hadlock or WHO Intergrowth standards. Always confirm with your obstetrician's growth scan report.
🧪 IVF Due Date by Transfer Day
Quick reference — add these days to your embryo transfer date to get the estimated due date (EDD).
Transfer Type
Embryo Age
Days to Add
Conception Date Offset
Day 2 transfer
2 days post-fertilisation
+264 days to get EDD
Transfer date − 2 days
Day 3 transfer
Cleavage stage
+263 days to get EDD
Transfer date − 3 days
Day 5 transfer (blastocyst)
Blastocyst — most common FET
+261 days to get EDD
Transfer date − 5 days
Day 6 transfer (extended)
Extended blastocyst culture
+260 days to get EDD
Transfer date − 6 days
Formula: EDD = Transfer Date + (266 − Embryo Age). Verified against ACOG and FOGSI IVF dating guidelines.
❓ Frequently Asked Questions
Common questions about conception date, pregnancy timing, IVF, and fetal development.
The conception date is the estimated day when fertilisation occurred — when sperm successfully met the egg in the fallopian tube, marking the beginning of pregnancy. Since sperm can survive 3–5 days in the reproductive tract, and the egg survives 12–24 hours after ovulation, the actual conception date is usually within a window of several days around ovulation. For most pregnancies, it is an estimate (±3–5 days). It is precisely known only in IVF, where fertilisation happens in a lab dish on a documented date.
Subtract 266 days from your due date. A pregnancy lasts 40 weeks (280 days) from the LMP, but since conception occurs approximately 2 weeks after LMP, the actual conception-to-birth duration is 38 weeks = 266 days.
Example: Due date is 15 November 2025 → subtract 266 days → Conception date ≈ 23 February 2025.
Use the calculator above (tab: "From Due Date") for an instant calculation.
Add 14 days to your conception date to estimate your LMP equivalent. Then count the weeks from that date to today.
Alternatively: Days since conception ÷ 7 = Conception weeks. Add 2 weeks to convert to gestational age (standard clinical measure).
Example: Conceived 1 January, today is 1 April = 90 days since conception = ~12.8 conception weeks = ~14.8 gestational weeks.
They are very close but not always identical. Ovulation is when the egg is released from the ovary. Fertilisation (conception) occurs when a sperm successfully penetrates the egg, typically within 12–24 hours of ovulation. Because sperm can survive 3–5 days in the fallopian tube, intercourse several days before ovulation can still result in conception. In clinical practice, ovulation date and conception date are used interchangeably as rough estimates.
A conception window (±5 days) can help narrow the timeline of when intercourse was most likely to have resulted in pregnancy. However, because of sperm survival (3–5 days) and natural ovulation variation, a conception date calculator alone cannot definitively determine paternity.
The only medically reliable method for paternity determination is DNA testing — either a prenatal Non-Invasive Prenatal Paternity (NIPP) test (from 8–9 weeks gestation) or a postnatal DNA test. A doctor can provide a conception timeline report but this is used alongside, not instead of, DNA evidence.
In IVF, fertilisation occurs outside the body in a laboratory dish, on a documented date. The conception date is simply: Transfer Date − Embryo Age (days). For a Day 5 blastocyst transfer on 10 March → Conception date = 5 March. This makes IVF the most precise method of pregnancy dating — there is no ovulation timing uncertainty. The EDD is then Conception Date + 266 days, or equivalently, Transfer Date + 261 days (Day 5).
Gestational age (GA) is measured from the first day of the last menstrual period (LMP) — it is the standard in all clinical reports, ultrasound scans, and Indian government maternal health documents (MCP card).
Conception age (fetal/embryonic age) is measured from actual fertilisation — always approximately 2 weeks less than gestational age.
Why it matters: When your obstetrician says "you are 12 weeks," they mean 12 gestational weeks (from LMP). The fetus is biologically only about 10 weeks old. This is why knowing the distinction matters when reading ultrasound reports or comparing data from different sources.
Accuracy depends on the method used:
• From due date: ±3–5 days (depends on how the original due date was calculated)
• From LMP: ±5–7 days for regular cycles; less accurate for irregular cycles
• From IVF transfer: Exact (±0 days) — fertilisation date is documented
• From ultrasound (CRL, 7–13 weeks): Most accurate for natural pregnancy — ±3–5 days
All conception calculators provide estimates. First-trimester ultrasound (crown-rump length, 7–13 weeks) is the gold standard for pregnancy dating per FOGSI, ACOG, and WHO guidelines.
Fetal size progresses from a poppy seed at 4 weeks (~1mm) to a watermelon at 40 weeks (~51cm, ~3.4kg). Key size milestones: kidney bean at 8 weeks, lime at 12 weeks (NT scan), avocado at 16 weeks, banana at 20 weeks (anomaly scan), ear of corn at 24 weeks, eggplant at 28 weeks, and watermelon at full term (40 weeks). See the detailed week-by-week table above for Hadlock chart-based measurements used in Indian obstetric practice.
Step 1: Note your conception date (from this calculator or from your first trimester ultrasound report).
Step 2: Add 14 days to get the equivalent "LMP date" (since conception is ~14 days after LMP in a 28-day cycle).
Step 3: Count weeks from that date to today.
Or simply use the "From LMP" tab on this calculator — enter the first day of your last period and your cycle length, and it will show you both conception date and current gestational age simultaneously.
⚠ Medical Disclaimer: This calculator provides estimated conception dates for informational purposes only. Conception dates are inherently estimates due to natural variability in ovulation timing and sperm survival. Clinical pregnancy dating must be confirmed by a registered obstetrician or gynaecologist using ultrasound (crown-rump length, 7–13 weeks). This tool does not replace medical advice, clinical judgement, or formal genetic / paternity testing. All calculations follow FOGSI, WHO, and ACOG obstetric dating guidelines.