End of 1st Trimester
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Estimated Due Date
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Enter a valid LMP date.
Pregnancy Progress
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Trimester Snapshot
Conception
Week --
Week 40
Current Trimester
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Days Until Due Date
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Estimated Conception
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Full Term Starts
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Important Milestones
Pregnancy Timeline
Mid-Pregnancy Scan
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Start of 3rd Trimester
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Full Term
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Milestone Schedule
Key Pregnancy Dates
| Milestone | Timing | Date | Status |
|---|
Formula Blueprint
How the Estimate Works
Naegele's rule sets the baseline, then cycle length shifts the full timeline earlier or later.
Standard Due Date
Due Date = LMP + 280 days
The standard estimate assumes a 28-day cycle and ovulation about 14 days after the start of the last period.
Cycle Adjustment
Adjusted Due Date = LMP + 280 + (Cycle Length - 28)
Longer cycles shift the estimate later. Shorter cycles shift it earlier by the same number of days.
Gestational Age
Gestational Age = Today - LMP
Pregnancy age is counted from LMP, not estimated conception date, which is why the timeline starts before ovulation.
LMPFirst day of the last menstrual period
280 days40 gestational weeks in the standard model
Cycle Length - 28Shift applied for non-average cycle timing
Pro Tips
Use the Estimate Carefully
Bring this estimate to prenatal appointments, but expect ultrasound dating and clinical context to refine the timeline if your cycle is irregular.
Planning
Track Milestones, Not Just the Due Date
Most planning decisions hinge on trimester changes, anatomy scan timing, and the full-term window, not only the final estimated date.
Reality Check
The Due Date Is a Window
Normal delivery can still happen weeks before or after the estimate, so use the calculator as a planning anchor rather than a guaranteed arrival day.
Common Questions
Due Date Calculator FAQ
Quick answers about LMP dating, gestational age, cycle adjustments, and pregnancy milestones.
How does a due date calculator work?
A due date calculator estimates your expected delivery date by adding 280 days, or 40 weeks, to the first day of your last menstrual period. This follows Naegele's rule, the standard baseline used by most providers.
How accurate is a pregnancy due date calculator?
A due date calculator gives a strong estimate, but only a small percentage of babies arrive on the exact projected date. Most full-term deliveries happen within a window around the estimate, and first-trimester ultrasound can refine it further.
What is the LMP method for calculating a due date?
The LMP method starts with the first day of your last menstrual period, assumes ovulation near day 14 of a 28-day cycle, and adds 280 days from that point. If your cycle is not 28 days, the estimate should be adjusted.
Can I calculate my due date if I have an irregular cycle?
Yes. A useful calculator adjusts for average cycle length that runs longer or shorter than 28 days. Longer cycles usually move ovulation and the due date later, while shorter cycles pull the estimate earlier.
How do I calculate my due date from my last period?
Using Naegele's rule, take the first day of your last period, add seven days, subtract three months, and add one year. This tool performs the same calculation instantly and then applies cycle-length adjustment when needed.
What is the difference between gestational age and fetal age?
Gestational age counts from the first day of your last menstrual period. Fetal age counts from estimated conception, which is usually about two weeks later. Clinical timelines and due date tools generally use gestational age.
How many weeks is a full-term pregnancy?
Full term is generally considered 39 weeks 0 days through 40 weeks 6 days. Birth between 37 and 38 weeks is often classified as early term, while pregnancy beyond 41 weeks may be considered late term.
Can my due date change during pregnancy?
Yes. Providers may revise the estimate based on first-trimester ultrasound measurements, especially when the scan differs meaningfully from the LMP-based estimate.
What if I do not remember the exact date of my last period?
If the date is uncertain, use the closest estimate you can recall for a starting point. An early ultrasound can help your provider determine gestational age more accurately.
How is a due date calculated with IVF?
IVF pregnancies are commonly dated from embryo transfer rather than LMP. A fertility specialist usually provides the correct adjusted timeline, so IVF estimates should follow clinical guidance instead of a standard LMP-only model.
What trimester am I in based on my due date?
The first trimester runs through week 12, the second covers weeks 13 through 27, and the third starts at week 28. Once the timeline is known, your current trimester follows directly from gestational age.
Does cycle length affect my due date?
Yes. The 280-day model assumes a 28-day cycle, so earlier or later ovulation shifts the estimate. That is why the calculator asks for average cycle length instead of using a one-size-fits-all date.
What is Naegele's rule?
Naegele's rule is the standard formula used to estimate a due date from the first day of the last menstrual period. It remains the basis of most online due date calculators and many provider-side baseline estimates.
How early or late can a baby be born and still be considered normal?
Birth between 37 and 42 weeks is generally considered within the normal range. Before 37 weeks is preterm, and after 42 weeks is post-term, both of which may require added medical monitoring.
Can I use a due date calculator to plan maternity leave?
Yes. The estimate is useful for planning leave, childcare, and appointments, but it should be treated as a planning window rather than a guaranteed delivery appointment.
Is the Due Date Calculator on NerdCalc free to use?
Yes. It is free, requires no sign-up, and updates instantly as you change the LMP date or cycle length.
How is a due date different from a delivery date?
A due date is an estimated date of delivery, not a guaranteed one. The actual delivery date depends on individual pregnancy factors, labor timing, and provider guidance.
What pregnancy milestones can I track using my due date?
Once the estimate is set, you can map trimester changes, anatomy scan timing, full-term milestones, and the broader pregnancy timeline from early gestation through delivery.
Data Integrity
Methodology and source verification
The timeline math on this page is cross-checked against ACOG guidance on estimating gestational age and due date, standard 280-day pregnancy dating, and term-pregnancy definitions. The calculator estimates an expected delivery date and milestone windows, but it does not replace ultrasound dating, IVF-specific dating, or clinical guidance from your prenatal care team.
Verified
Reference basis: the calculation engine applies Naegele's rule to the first day of the last menstrual period, adjusts for user-entered cycle length, and derives gestational milestones from standard obstetric week ranges. The explanatory copy is anchored to ACOG clinical guidance, patient guidance, and term-pregnancy definitions used in obstetric practice.
ACOG: Methods for Estimating the Due Date
Used for the dating hierarchy, the role of first-trimester ultrasound, and the handling of ART or IVF pregnancies.
Read the ACOG due-date guidanceACOG: When Pregnancy Goes Past Your Due Date
Used for the 280-day baseline, EDD framing, and patient-facing explanation of how due dates are selected and interpreted.
Read the ACOG FAQACOG: Definition of Term Pregnancy
Used for the early term, full term, late term, and postterm milestone language shown in due-date interpretation.
View term pregnancy definitionsACOG App estimated due date calculator
Used to confirm that ACOG's own calculator framework relies on LMP and the first accurate ultrasound for estimated due date assignment.
See ACOG app calculator details