- Estimated due date
- 2027-04-07
- Gestational age on selected date
- 14 weeks, 2 days
- Estimated conception
- 2026-07-15
How it works
Weeks and days are not decimals
An ultrasound age of 8 weeks 6 days means 62 gestational days, not 8.6 weeks. Enter weeks and days in their separate fields; confusing the formats can shift the calculated pregnancy timeline by days.
Choosing the pregnancy dating information you know
Select the dating mode that matches the information available, such as a menstrual date, IVF transfer, ultrasound dating, or a known due date. These inputs represent different starting points and should not be substituted for one another. The calculated timeline is an estimate under the selected method. It does not confirm a pregnancy or replace dating and follow-up by a maternity care professional.
Last menstrual period: formula and assumptions
Estimated due date = LMP + 280 days + (cycle length−28).
Gestational age is conventionally counted from the last menstrual period. Ultrasound and clinical assessment can revise the estimate.
Conception date: formula and assumptions
Estimated due date = conception + 266 days.
A conception date is generally an estimate unless linked to assisted reproduction.
IVF transfer: formula and assumptions
Estimated due date = transfer date + 266 − embryo age days.
Confirm assisted-reproduction dates with your treating clinic.
Ultrasound dating: formula and assumptions
Estimated due date = scan date + (280−gestational days).
Use the gestational age supplied in the clinical ultrasound report.
From a known due date: formula and assumptions
Estimated conception=due date−266 days; conventional gestational start=due date−280 days.
This reverses a 40-week dating convention. It does not establish an exact conception date.
Worked example
Using the Last menstrual period example:
- First day of last menstrual period
- 2026-07-01
- Typical cycle length (days)
- 28
- Calculate gestational age on
- 2026-10-09
Estimated due date = LMP + 280 days + (cycle length−28).
Example result
Estimated due date: 2027-04-07
Gestational age on selected date: 14 weeks, 2 days
Estimated conception: 2026-07-15
These are illustrative inputs. Change the values to explore a different scenario.
What to keep in mind
Dates are estimates, not a prediction of the exact day of delivery.
Formula references
References explain the underlying methods; they do not imply endorsement or individual professional review of Finflo.
Common questions
Why does gestational age start before the estimated conception date?
Conventional gestational dating counts from the last menstrual period, rather than from conception itself.
Can the calculated due date change after a clinical assessment?
Yes. Ultrasound and clinical information can revise an estimate. A due date does not predict the exact day of delivery.
Prepared by Finflo. See our methodology and editorial policy. Read the relevant professional-advice limitations.