Due Date Calculator
Estimate your pregnancy due date using the first day of your last menstrual period, a known conception date, or an IVF embryo-transfer date. The calculator also shows estimated gestational age, conception date, trimester milestones and pregnancy progress.
Choose a Calculation Method
Select the pregnancy dating information you know best.
Pregnancy Progress
Progress is based on a 40-week gestational pregnancy timeline.
Estimated Pregnancy Milestones
Dates are calculated from the estimated LMP-equivalent date.
Pregnancy Due Date Calculation Methods
Different dating methods use different known dates but are converted to the same approximate 40-week gestational framework.
| Method | Calculation | Approximate Pregnancy Length |
|---|---|---|
| Last menstrual period | LMP + 280 days | 40 weeks |
| Known conception date | Conception + 266 days | About 38 weeks after conception |
| IVF 3-day embryo | Transfer + 263 days | Equivalent to 266 days from fertilisation |
| IVF 5-day embryo | Transfer + 261 days | Equivalent to 266 days from fertilisation |
How to Use the Due Date Calculator
Choose the dating method that matches the information you know.
You can calculate an estimated due date from:
- The first day of your last menstrual period;
- A known conception date; or
- An IVF embryo transfer date.
How Is a Pregnancy Due Date Calculated From LMP?
Pregnancy is traditionally dated from the first day of the last menstrual period rather than from the date of conception.
This is equivalent to approximately 40 weeks.
What Is Naegele’s Rule?
Naegele’s Rule is a traditional method for estimating a pregnancy due date from the first day of the last menstrual period.
A simplified version is:
This is approximately equivalent to adding 280 days.
How Does Cycle Length Affect the Due Date?
The standard LMP calculation assumes a 28-day menstrual cycle.
If your average cycle is longer or shorter, the calculator adjusts the estimated due date by the difference from 28 days.
How Is Due Date Calculated From Conception?
When conception date is known, the estimated due date is approximately:
That corresponds to approximately 38 weeks after conception.
Why Is Pregnancy 40 Weeks if Conception Was Only 38 Weeks Ago?
Gestational age is traditionally counted from the first day of the last menstrual period, which is usually about two weeks before conception in a typical 28-day cycle.
Therefore:
How Is an IVF Due Date Calculated?
IVF dating can be more precise because the embryo-transfer date and embryo age are known.
5-Day Embryo Transfer
3-Day Embryo Transfer
How Is Pregnancy Week Calculated?
Pregnancy week is based on gestational age measured from the LMP-equivalent date.
For example:
- 7 days = 1 week pregnant;
- 70 days = 10 weeks pregnant;
- 140 days = 20 weeks pregnant;
- 280 days = 40 weeks pregnant.
What Does 20 Weeks Pregnant Mean?
At 20 weeks gestational age, approximately half of the standard 40-week pregnancy timeline has elapsed.
This does not necessarily mean conception occurred exactly 20 weeks earlier, because gestational age includes approximately two weeks before conception in a typical cycle.
Pregnancy Trimesters
Pregnancy is commonly divided into three trimesters.
- First trimester: approximately Weeks 1–13;
- Second trimester: approximately Weeks 14–27;
- Third trimester: approximately Week 28 until birth.
Exact definitions can vary slightly between clinical sources.
Is the Due Date the Exact Day the Baby Will Be Born?
No. A due date is an estimate rather than a prediction of the exact birth date.
Only a minority of babies are born exactly on the estimated due date.
Why Can an Ultrasound Due Date Be Different?
Ultrasound measurements, particularly early pregnancy measurements, may produce a different gestational-age estimate from an LMP calculation.
Clinical dating may be revised depending on ultrasound findings and individual circumstances.
Which Due Date Is More Accurate: LMP or Ultrasound?
This calculator cannot determine which dating method should be used clinically.
Healthcare professionals may use menstrual history, assisted-conception dates and ultrasound measurements together when determining the official pregnancy dating.
What If My Periods Are Irregular?
LMP-based dating may be less accurate when menstrual cycles are irregular or when ovulation does not occur around the expected time.
In such cases, ultrasound dating may provide additional information.
What If I Don’t Know My Last Period?
If the last menstrual period is unknown, pregnancy dating may use other information such as ultrasound measurements, a known conception date or assisted-reproduction dates.
Can I Calculate Due Date From Ovulation?
If you have a reliable estimate of ovulation or conception date, you can use the conception-date method.
A due date is approximately 266 days after conception.
For estimated ovulation timing, use the Ovulation Calculator.
Can I Calculate Due Date From IVF?
Yes. This calculator includes both 3-day and 5-day embryo transfer methods.
Because embryo age is known, IVF pregnancy dating does not rely on an estimated ovulation date.
How Accurate Is a Due Date Calculator?
A due date calculator provides an estimate based on standard pregnancy dating conventions.
Actual clinical dating may differ because of:
- Irregular cycles;
- Uncertain LMP date;
- Variation in ovulation timing;
- Ultrasound findings;
- IVF or assisted reproduction; and
- Individual clinical circumstances.
Due Date Calculator Assumptions
This calculator:
- Uses 280 days from LMP for a standard 28-day cycle;
- Adjusts LMP dating for entered cycle length;
- Uses 266 days from conception;
- Uses 263 days from a 3-day embryo transfer;
- Uses 261 days from a 5-day embryo transfer;
- Calculates gestational age from an LMP-equivalent date;
- Uses a 40-week pregnancy timeline;
- Provides estimates only;
- Does not replace ultrasound dating; and
- Does not provide medical diagnosis or obstetric advice.
Related Pregnancy Calculators
Due Date Calculator FAQs
How is pregnancy due date calculated?
A common method adds 280 days to the first day of the last menstrual period. The calculator can also use conception or IVF transfer dates.
How many weeks is pregnancy?
Pregnancy is conventionally dated as approximately 40 weeks from the first day of the last menstrual period.
How do I calculate due date from conception?
Add approximately 266 days to the conception date.
How do I calculate an IVF due date?
For a 5-day embryo transfer, add 261 days to the transfer date. For a 3-day embryo transfer, add 263 days.
Does cycle length change the due date?
It can. The standard LMP formula assumes a 28-day cycle, so this calculator adjusts the date when a different average cycle length is entered.
Is the calculated due date exact?
No. A due date is an estimate and actual birth may occur before or after the estimated date.
Can ultrasound change my due date?
Clinical pregnancy dating may be revised based on ultrasound measurements and individual circumstances.