Pregnancy Timeline Calculator
Start with the pregnancy record you already have. One workflow can use a current recorded due date, a reliable last menstrual period (LMP), a well-supported ovulation date, a documented fertilization date, or pregnancy weeks and days recorded on a specific date.
The result keeps your entered record separate from derived and approximate dates, then shows one coherent pregnancy calendar: estimated due date (EDD), weeks and days, trimester, key calendar milestones, and an optional comparison with a second record.
Have a Day-3 or Day-5 embryo-transfer record? Use the IVF Due Date Calculator. IVF dating remains a separate treatment-record workflow.
Transparent, browser-based pregnancy and preconception calculators and reference tools for educational use.
What this record resolver returns
The resolver answers several connected calendar questions without pretending that every date has the same evidentiary status. It shows the record used, a pregnancy-calendar start, an EDD, pregnancy weeks and days today, pregnancy age on an optional selected date, trimester, and a short milestone timeline.
- RECORDED identifies an EDD or pregnancy-age record entered from the current pregnancy record.
- USER-ENTERED identifies a date or value supplied by the user.
- DERIVED identifies calendar arithmetic from that record.
- APPROXIMATE identifies an around-date estimate that cannot establish an exact biological event.
A pregnancy-calendar start can be a derived counting reference. Unless it is the reliable LMP actually entered, it is not another reported menstrual period.
How each supported record is resolved
| Record available | Calendar rule | What the workflow can show |
|---|---|---|
| Current recorded EDD | Start = EDD − 280 days | Weeks, trimester, milestones, and an around conception estimate |
| LMP + supported average cycle | EDD = LMP + 280 + (cycle − 28) days | Cycle-adjusted pregnancy calendar and around conception estimate |
| Well-supported ovulation | EDD = ovulation + 266 days | Pregnancy calendar without relabeling ovulation as conception |
| Documented fertilization | EDD = fertilization + 266 days | Pregnancy calendar with the entered fertilization date preserved |
| Dated completed weeks + days | Start = record date − gestational age; EDD = start + 280 days | The calendar implied by that dated record |
The LMP cycle adjustment is a supported calendar model, not proof of an exact ovulation date. Substantial cycle variability or an uncertain LMP can make a simple estimate unsuitable.
Compare records without averaging them
If two records produce different EDDs, the comparison shows both records, both calculated dates, their provenance labels, and the absolute calendar-day difference. It does not average the dates and does not declare one record medically correct.
A current EDD in the pregnancy record, together with guidance from the prenatal or fertility care team, takes priority over an online calculation. Ask the care team about a discrepancy rather than repeatedly recalculating or redating the pregnancy yourself.
Clinical records and ultrasound remain separate
This workflow performs date-only calendar arithmetic. It does not interpret ultrasound measurements, apply ultrasound redating thresholds, assess fetal growth, confirm pregnancy location or viability, decide whether a discrepancy requires clinical review or redating, or decide whether an established EDD should change.
For a pregnancy following embryo transfer, use the embryo age, actual transfer date, and EDD recorded by the fertility clinic. This page deliberately sends documented Day-3 and Day-5 transfer records to the separate IVF workflow.
What this timeline cannot determine
- the exact day of ovulation, fertilization, intercourse, implantation, labor, or birth;
- pregnancy location, viability, fetal wellbeing, growth, parentage, or treatment outcome;
- whether a clinical EDD should be confirmed or revised; or
- what testing, medication, treatment, or delivery decision is appropriate.
Do not use this workflow to delay medical care or to replace instructions from a qualified healthcare professional.
Official sources and method mapping
Each source is listed for the specific statement it supports. These organizations do not review, certify, sponsor, or endorse Pregnancy Metrics.
- ACOG — Methods for Estimating the Due Date
Supports documenting the established gestational age and EDD, prioritizing ART records when applicable, using first-trimester ultrasound to establish or confirm gestational age, and limiting later EDD changes to rare, documented circumstances.
- ACOG — How Your Fetus Grows During Pregnancy
Supports counting gestational age from the first day of the last menstrual period, reporting completed weeks and additional days, and the conventional trimester boundaries used here.
- ACOG — When Pregnancy Goes Past Your Due Date
Supports the conventional 280-day pregnancy calendar counted from the first day of the last menstrual period and the EDD as a pregnancy-timing reference rather than a guaranteed birth date.
- Merck Manual Professional — Evaluation of the Obstetric Patient
Directly supports estimated delivery calculations using conception date plus 266 days and last menstrual period plus 280 days for regular 28-day cycles.
Shared constants, date-only arithmetic, supported boundaries, and versioning are documented in the Methodology.