How do due dates, pregnancy weeks, and conception estimates fit together?
Understand why pregnancy starts before conception, what completed weeks and days mean, and why LMP and ultrasound dates can differ.
Read the pregnancy dating guide →Plain-language explanations
Pregnancy & Preconception Blog
Pregnancy Metrics guides explain how pregnancy dates, weeks, conception, IVF, weight gain, home testing, and ovulation tracking work. They are educational explanations, not a pregnancy record, diagnosis, or substitute for clinical care.
Use this hub when you want to understand how something works or what a result means. Calculators answer “calculate from information I have”; guides explain the model, interpretation limits, and authoritative sources for one topic.
Find a guide from one question
Choose the concept you want to understand. The result points to one primary guide and names the boundary that guide cannot establish.
Choose one option to see the matching path and a useful detail.
This guide finder does not ask for or store pregnancy dates.
Choose a guide by your question
Start with the question you are trying to understand. These guides explain a model or evidence boundary; they do not require you to enter a pregnancy date.
Why does IVF dating use a Day-3 or Day-5 transfer record?
Understand embryo age at transfer, the 263- and 261-day offsets, fresh and frozen transfer records, and what IVF dating cannot predict.
Read the IVF dating guide →How do pregnancy weight-gain recommendations change with pre-pregnancy BMI?
Compare singleton and twin ranges, later-trimester rate context, and the boundary between population guidance and a personal target.
Read the weight-gain guide →How do cycle estimates, ovulation signs, and pregnancy-test timing fit together?
Understand approximate fertile timing, ovulation signs, expected-period context, when to test, early negatives, and recent-sex fallback timing.
Read the trying and testing guide →How these guide topics connect
The topics answer different questions and do not carry the same degree of certainty.
| Topic | Starts from | What it explains | Most important limit | Guide |
|---|---|---|---|---|
| Pregnancy dating explained | The pregnancy calendar, a last period, an estimated due date, or dated pregnancy weeks | Why pregnancy starts before conception, how weeks and due dates are counted, and why dates can differ | It cannot establish exact biological timing, fetal health, a guaranteed birth date, or whether an EDD should be changed | Pregnancy Dating Explained: Due Dates, Weeks & Conception |
| IVF dating | The transfer date and documented Day-3 or Day-5 embryo age | How embryo age and transfer date produce the IVF due date and pregnancy-calendar age | It cannot predict implantation, IVF success, viability, pregnancy outcome, or exact delivery timing | How IVF Due Dates Are Calculated |
| Pregnancy weight gain | Pre-pregnancy BMI and singleton or twin pregnancy type | Population-level total ranges and later-trimester rate context | A personal target, diagnosis, or fetal-growth assessment | Pregnancy Weight Gain Guidelines |
| Trying, ovulation and pregnancy-test timing | Cycle dates, ovulation signs, an expected period, DPO, or a recent-sex date | How fertile-window estimates, ovulation signs, expected-period context, and home-test timing relate without confirming a biological event | Exact ovulation, conception or implantation, pregnancy probability, diagnosis, or safe days | Trying, Ovulation and Pregnancy Test Timing |
Related concepts do not make the four guide topics interchangeable. Each guide should be interpreted according to the question and evidence it addresses.
Suggested reading paths
You do not need to read every guide. Use the path that matches what you are trying to understand.
General pregnancy dating
Start with the pregnancy calendar, then learn how the due date anchors that calendar.
I already have a recorded due date
Use the current recorded due date rather than recalculating or averaging older dates.
IVF or frozen embryo transfer
IVF dating starts from the embryo-transfer record, not from an ordinary menstrual-cycle estimate.
Pregnancy weight gain
Start with the published BMI-based ranges, then use the calculator only for transparent reference arithmetic.
Trying, ovulation and pregnancy-test timing
Connect cycle estimates, ovulation signs, expected periods, DPO, and home-test timing without turning estimates into confirmation or diagnosis.
I want the site-wide rules
Use Methodology for formulas, date-only arithmetic, supported inputs, boundaries, and update rules. Use Editorial and Methodology Review for the real evidence and release process.
All pregnancy and preconception guides
Each guide covers one defined topic in depth and links its factual claims to authoritative sources.
Pregnancy Dating Explained: Due Dates, Weeks & Conception
A plain-language guide to pregnancy weeks, due dates, conception estimates, ultrasound dating, and which due date to follow.
- Best for
- Understanding why pregnancy starts before conception and how weeks, due dates, conception estimates, and ultrasound dating fit together
- You will learn
- How pregnancy weeks are counted, how due dates are estimated, and which due date to follow when dates differ
- Does not establish
- Exact biological timing, a guaranteed birth date, fetal health, or whether a pregnancy should be clinically redated
How IVF Due Dates Are Calculated
Day-3 and Day-5 transfer dating, FET timing, pregnancy age on transfer day, and when to use the clinic’s established due date.
- Best for
- Understanding Day-3 and Day-5 transfer dating for fresh or frozen embryo-transfer records
- You will learn
- Why the transfer date is assigned 2w3d or 2w5d pregnancy-calendar age and why the due-date offsets are 263 or 261 days
- Does not establish
- Implantation, IVF success, viability, number of fetuses, pregnancy outcome, or exact delivery timing
Pregnancy Weight Gain Guidelines
A plain-language guide to singleton and twin weight-gain ranges, later-pregnancy rate context, and why individual recommendations can differ.
- Best for
- Understanding singleton and twin weight-gain ranges by pre-pregnancy BMI
- You will learn
- How singleton and twin ranges, later-pregnancy rate context, non-linear week-to-week change, and pre-pregnancy BMI fit together
- Does not establish
- A personal target, diagnosis, fetal growth, or treatment plan
Trying, Ovulation and Pregnancy Test Timing
A plain-language guide to ovulation estimates, fertile windows, pregnancy-test timing, early negatives, and recent-sex fallback timing.
- Best for
- Connecting cycle estimates, ovulation signs, expected periods, DPO, recent sex, and home-test timing
- You will learn
- How ovulation and fertile-window estimates relate to LH or OPK results, cervical mucus, BBT, pregnancy-test timing, early negatives, and the recent-sex fallback
- Does not establish
- Exact ovulation, conception or implantation, pregnancy probability, diagnosis, or safe contraception days
Choose the right Pregnancy Metrics resource
Need a calculator result from information you have?
Use the homepage calculator selector to start from the date, cycle information, pregnancy record, transfer record, or measurements you already have.
Need to understand how something works?
Use the guides on this page. They explain pregnancy dating, weight gain, home testing, and ovulation tracking without asking you to enter calculator inputs.
Need the exact formula and implementation rules?
Methodology documents constants, date-only arithmetic, supported inputs, boundaries, rounding, and update practices.
Need to understand review and maintenance?
Editorial and Methodology Review explains source selection, claim review, testing, release checks, and the absence of external clinician certification.
Review the Privacy Policy for data handling and the Medical Disclaimer for the limits of educational calendar tools.