Due Date Calculator
Estimate your due date, weeks pregnant, gestational age, trimester, conception date, and milestones from LMP, conception, ultrasound, IVF, or a confirmed due date.
Choose a dating method, enter the known information, and select Calculate.
Due Date Calculator
Important: This calculator provides an estimated due date, not a diagnosis or a guaranteed delivery date. Confirm pregnancy dating and care decisions with a qualified prenatal healthcare professional.
powered by CaliforniaCalculatorTMGet this for your site
What does the Due Date Calculator calculate?
The Due Date Calculator converts the values you enter into a structured estimate using the formulas and assumptions documented on this page. Use the result to compare scenarios, review the calculation details, and identify sensitive inputs. Check the guide and formula sections before using the estimate for an important decision.
At a Glance
- Estimate a due date from an existing due date, last menstrual period, conception, ultrasound, or IVF transfer.
- Use a user-entered as-of date for gestational age and pregnancy week.
- See estimated LMP, conception, trimester, progress, term dates, and a 42-week schedule.
- Compare visual charts with equivalent text and table values.
- Use calendar dates without hidden current-date assumptions.
- Confirm the best obstetric estimate with a qualified prenatal or fertility care professional.
History of Pregnancy Due Date Estimation
Pregnancy dating conventionally counts about 280 days from the first day of the last menstrual period, even though conception commonly occurs later. This convention provides a consistent gestational clock when conception is not directly known.
Modern obstetric dating also uses early ultrasound and assisted-reproduction records. ACOG recommends establishing and documenting the best obstetric estimate after menstrual and first accurate ultrasound information are available.
What This Due Date Calculator Does
The calculator converts the selected dating method into an estimated due date. It then works backward 280 days for an estimated LMP and 266 days for estimated conception. The entered as-of date determines completed gestational weeks, additional days, current pregnancy week, trimester, progress, remaining days, term milestones, and the weekly calendar.
Who Should Use It
For “Who Should Use It,” the Pregnancy Due Date Calculator organizes the relevant inputs, applies the documented method, and shows a result that can be compared across scenarios. The points below identify the specific considerations and assumptions users should review before relying on the estimate.
- People who want to understand a clinician-confirmed due date on a calendar.
- People estimating from an LMP and average cycle length.
- People with a known conception or ovulation date.
- People reproducing a gestational age recorded at an ultrasound.
- IVF patients working from a transfer date and embryo age.
- Students learning how pregnancy dating methods relate.
The calculator cannot confirm pregnancy, assess fetal growth, decide whether a pregnancy should be redated, or replace prenatal care.
Problems It Solves
- Keeps five dating methods in one consistent calendar model.
- Adjusts LMP dating for an entered cycle length.
- Converts ultrasound weeks and days into remaining gestational days.
- Accounts for embryo age in IVF transfer dating.
- Separates completed gestational age from the numbered week in progress.
- Builds term milestones and a 42-week schedule from the same due date.
Key Benefits
Every personal date and dating assumption is entered by the user. The same tested engine powers the calculator, examples, widget, calendar schedule, and PDF report. The charts do not introduce a second gestational timeline.
Pregnancy Dating Definitions
- EDD
- Estimated due date, the 40-week calendar estimate used by the calculator.
- LMP
- First day of the last menstrual period used as gestational day zero.
- Gestational age
- Completed weeks and additional days since the estimated LMP.
- Pregnancy week
- The numbered week currently in progress. At 22 weeks 5 days, week 23 is in progress.
- As-of date
- The user-entered calendar date on which progress and gestational age are calculated.
- Best obstetric estimate
- The documented clinical estimate based on the available menstrual, ultrasound, or assisted-reproduction information.
Pregnancy Dating Methods
| Information available | Calculator method | Required entry |
|---|---|---|
| Documented EDD | Due date | Estimated due date |
| First day of last period | Last menstrual period | LMP and average cycle length |
| Known conception or ovulation | Conception | Conception date |
| Dated ultrasound | Ultrasound | Scan date and gestational weeks plus days |
| Embryo transfer | IVF | Transfer date and embryo age |
Use dates documented by the prenatal or fertility care team when they differ from a simple calendar reconstruction.
Understanding Gestational Age and Pregnancy Week
A gestational age of 12 weeks 4 days means 12 complete weeks and 4 additional days have elapsed. Pregnancy week 13 is in progress. This distinction explains why the displayed pregnancy week is one greater than completed weeks.
Trimesters and Term Milestones
The calculator assigns the first trimester through 13 weeks 6 days, the second from 14 weeks 0 days through 27 weeks 6 days, and the third from 28 weeks onward. It places early term at 37 weeks, full term at 39 weeks, late term at 41 weeks, and postterm at 42 weeks.
These are calendar classifications, not predictions of when labor will begin.
When to Use It
Use the calculator to reproduce a documented date, compare compatible source dates, understand pregnancy week on a chosen date, or build an educational pregnancy calendar. Use realistic inputs and review the Pregnancy Due Date Calculator assumptions before relying on this result for decisions.
Use the Ovulation Calculator for fertile-window estimates. Neither calculator confirms pregnancy or replaces clinical dating.
How the Calculation Works
For “How the Calculation Works,” the Pregnancy Due Date Calculator organizes the relevant inputs, applies the documented method, and shows a result that can be compared across scenarios. The points below identify the specific considerations and assumptions users should review before relying on the estimate.
- The engine validates the selected method and its required dates or whole-number inputs.
- The method is converted to an estimated due date.
- The engine subtracts 280 days for estimated LMP and 266 days for estimated conception.
- Elapsed whole days are calculated from estimated LMP to the entered as-of date.
- Completed weeks and remaining days are derived by division by seven.
- Trimester, progress, remaining days, and term milestones use the same elapsed-day count.
- The engine creates 42 consecutive week rows from the estimated LMP.
Common Due Date Calculator Mistakes
- Entering the last day of a period instead of the first day.
- Using today automatically instead of checking the as-of date.
- Treating an estimated conception date as a confirmed event.
- Entering ultrasound age for a different scan date.
- Forgetting embryo age when using an IVF transfer.
- Assuming pregnancy week and completed gestational weeks are identical labels.
- Treating the EDD as a guaranteed delivery day.
- Using a calendar estimate to override a documented obstetric estimate.
Frequently Asked Questions
How long does pregnancy last?
An average pregnancy lasts about 40 weeks, or 280 days, beginning with the first day of the last menstrual period. This is approximately 38 weeks from conception. Review the Pregnancy Due Date Calculator assumptions before relying on this result for decisions.
How is my pregnancy due date calculated?
A due date may be estimated using the first day of the last menstrual period, ultrasound measurements, conception information, an existing due date, or IVF treatment dates. Review the Pregnancy Due Date Calculator assumptions before relying on this result for decisions.
Can an ultrasound change my due date?
An early ultrasound may confirm or adjust the estimated due date when it differs significantly from menstrual dating or the last menstrual period is uncertain. Use realistic inputs and review the Pregnancy Due Date Calculator assumptions before relying on this result for decisions.
Is the due date the exact day my baby will be born?
No. A due date is an estimate based on gestational dating. Labor may begin before or after that date. For a useful Pregnancy Due Date Calculator result, use realistic inputs, compare relevant scenarios, and review the stated assumptions before making a decision.
Why is pregnancy counted as 40 weeks?
Pregnancy weeks are counted from the first day of the last menstrual period, approximately two weeks before conception commonly occurs. For a useful Pregnancy Due Date Calculator result, use realistic inputs, compare relevant scenarios, and review the stated assumptions before making a decision.
What does 12 weeks pregnant mean?
It means that 12 gestational weeks have passed since the first day of the last menstrual period, even though conception may have occurred approximately 10 weeks earlier. Review the Pregnancy Due Date Calculator assumptions before relying on this result for decisions.
When does the first trimester end?
The first trimester generally continues through approximately week 13. Clinical and educational resources may place trimester boundaries slightly differently. For a useful Pregnancy Due Date Calculator result, use realistic inputs, compare relevant scenarios, and review the stated assumptions before making a decision.
When is a pregnancy considered full term?
A pregnancy is classified as full term from 39 weeks and 0 days through 40 weeks and 6 days. For a useful Pregnancy Due Date Calculator result, use realistic inputs, compare relevant scenarios, and review the stated assumptions before making a decision.
What is a late-term pregnancy?
Late term refers to 41 weeks and 0 days through 41 weeks and 6 days. For a useful Pregnancy Due Date Calculator result, enter realistic values, compare relevant scenarios, check the calculation details, and review the definitions, assumptions, and limitations before using the estimate for an important decision.
What is a postterm pregnancy?
Postterm refers to a pregnancy that has reached 42 weeks and 0 days or later. For a useful Pregnancy Due Date Calculator result, enter realistic values, compare relevant scenarios, check the calculation details, and review the definitions, assumptions, and limitations before using the estimate for an important decision.
When should I take a pregnancy test?
A home pregnancy test may be taken around the time of a missed period. Testing after the first day of the missed period and carefully following the instructions can improve reliability. Review the Pregnancy Due Date Calculator assumptions before relying on this result for decisions.
Can I exercise while pregnant?
Moderate activity is considered safe for many people with healthy pregnancies. Current U.S. guidance recommends approximately 150 minutes per week, but individual restrictions should be discussed with a prenatal healthcare professional. Review the Pregnancy Due Date Calculator assumptions before relying on this result for decisions.
How much weight should I gain during pregnancy?
The recommended range depends on prepregnancy BMI, whether one baby or multiples are expected, and individual health factors. For a useful Pregnancy Due Date Calculator result, use realistic inputs, compare relevant scenarios, and review the stated assumptions before making a decision.
Can I take medicine while pregnant?
Some medicines may be appropriate and necessary during pregnancy, while others may require changes. Consult a healthcare professional before starting, stopping, or changing any medication. Use realistic inputs and review the Pregnancy Due Date Calculator assumptions before relying on this result for decisions.
One Useful Fact
When source dates describe the same pregnancy timeline, LMP plus 280 days, conception plus 266 days, compatible ultrasound dating, and IVF transfer dating can all converge on the same estimated due date.
Conclusion
A due date calculator is most useful for understanding the calendar behind an existing estimate. Choose the method that matches the information actually available, verify the as-of date, and use the result as education alongside professional prenatal guidance.