Quick answer
Due Date Calculator: what it calculates
Due Date Calculator calculates estimated due date from first day of last period and average cycle length. The visible formula is Due date = first day of last period + 280 days + cycle adjustment.
Health Calculators
Due Date Calculator
Use this due date calculator to estimate a pregnancy due date from the first day of the last menstrual period and average cycle length.
Last reviewed June 6, 2026Source note includedPlanning estimateNo expert review claimed
Live calculator
Due date calculator
Estimated due dateFeb 5, 2027
Based on last menstrual period plus 280 days, adjusted for cycle length.
Estimated conceptionMay 15, 2026
Approximate ovulation timing for planning context.
Weeks pregnant8.3 weeks
First trimester estimate ends around Aug 6, 2026.
Use this as a planning estimate, not medical advice. Medical conditions, medication, pregnancy, eating disorder history, or disease-specific nutrition needs should be handled with a qualified professional.
ResultEstimated due date
InputsFirst day of last period, Average cycle length
FormulaDue date estimate
Formula
Due date estimate
Due date = first day of last period + 280 days + cycle adjustmentThis is a common estimate and does not replace ultrasound dating or medical care.
How to use
Steps
- Enter the first day of the last menstrual period.
- Enter average cycle length.
- Review estimated due date and conception timing.
- Confirm important pregnancy dates with a qualified clinician.
Example
Sample calculation
Last periodMay 1, 2026
Cycle length28 days
Estimated due dateFeb 5, 2027
Calculator use
Best for
- Use this due date calculator to estimate a pregnancy due date from the first day of the last menstrual period and average cycle length.
- Estimating due date, pregnancy week, trimester, or conception timing for planning conversations.
- Checking date assumptions from last menstrual period, due date, or cycle length with the method visible.
- Preparing non-diagnostic timing context before confirming dates with a qualified clinician.
Before relying on it
Check first
- Treating pregnancy date estimates as diagnosis, medical advice, or a substitute for clinician dating.
- Ignoring cycle variability, ultrasound timing, fertility treatment dates, irregular periods, or clinician guidance.
- Using late or uncertain dates as if they were exact conception or due-date proof.
Details
What to know before using the result
These notes make the assumptions explicit, especially where the same search query can mean slightly different things.
Dating methodLMP plus 280 days
The estimate starts from the first day of the last menstrual period and adds about 40 weeks.
Cycle lengthRough adjustment
Longer or shorter average cycles can shift estimated ovulation timing, but irregular cycles can make dating less reliable.
Clinical datingConfirm with clinician
A clinician may update the estimated due date based on ultrasound, assisted reproduction dates, or other clinical information.
Benchmarks
How to read the result
The calculator is a decision aid, not a fixed rule. Use the output to compare scenarios and document your assumptions. Benchmark ranges are broad planning heuristics unless this page names a specific source for the range.
280 days: Standard estimate.
A common due date estimate from last menstrual period.
Cycle adjustment: Personalized.
Longer or shorter cycles can shift the estimate.
Ultrasound: Clinical dating.
Medical dating can differ from calculator estimates.
Calculator accuracy
Methodology and assumptions
The formula, inputs, example, and limitations are shown so the result is checkable, not just a number in a box.
Formula
Due date = first day of last period + 280 days + cycle adjustment
Inputs used
First day of last period, Average cycle length
Limitations
Health results are screening or planning estimates. Age, body composition, medication, medical history, pregnancy, and professional guidance can change the right interpretation.
Last reviewed
June 6, 2026
Cite this page
Toolkit Shelf. Due Date Calculator. Last reviewed June 6, 2026. https://toolkitshelf.com/tools/due-date-calculator
FAQ
Common questions
How is a pregnancy due date estimated?
A common estimate adds 280 days to the first day of the last menstrual period, adjusted for cycle length.
Is this due date exact?
No. It is an estimate. A clinician may use ultrasound and medical history for dating.
Why does cycle length matter?
Cycle length can shift estimated ovulation timing, which can shift the due date estimate.
When should I ask a clinician?
Ask a clinician or qualified nutrition professional when pregnancy, medication, medical history, eating disorder risk, symptoms, or disease-specific guidance matters.
Why can health formulas be misleading?
Health formulas simplify age, sex, body composition, training status, measurement method, pregnancy, and medical context into a planning estimate.
Is this medical advice?
No. Health calculators are screening or planning tools and do not diagnose, treat, or replace professional medical or nutrition guidance.