Health Tools
Pregnancy Due Date and Gestational Age Calculator from LMP
Estimate a due date with the conventional LMP + 280-day method and count complete weeks plus remaining days on a selected date, with a visible warning that ultrasound and clinical assessment may confirm or revise pregnancy dating.
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Pregnancy Due Date and Gestational Age Calculator
Inputs remain in this page only. They are not saved, placed in the URL, or sent to THcount.
Calendar estimate
Due date and gestational age
Privacy: Weight, energy, sleep times and pregnancy dates are processed only in this page's memory. No account, cookie, analytics event, browser storage or server log receives them.
Quick answer
How are due date and gestational age calculated from the last menstrual period?
The conventional LMP estimated due date (EDD) is the first day of the last menstrual period plus 280 days, or 40 weeks. Gestational age on a selected date is the number of days since LMP expressed as complete weeks and remaining days. It is an estimate that needs professional confirmation, especially when LMP is uncertain, cycles are irregular, assisted reproduction was used, or ultrasound dating is available.
How to use this tool
- Enter the first day of the last menstrual bleeding, not an intercourse date or estimated conception date
- Choose the date on which to calculate gestational age, from LMP through 42 weeks later
- Read EDD, gestational age and the LMP-method boundary, then rely on professionally confirmed clinical dating; export Print, Excel, PDF, TXT or PNG only if useful
How the calculation works
Dates are handled as calendar dates without local-time shifts. EDD = LMP epoch day + 280. Gestational age = as-of date − LMP, divided by 7 into complete weeks and remaining days. The as-of date is limited from LMP through 42 weeks. This tool does not adjust for cycle length, intercourse date, ultrasound or IVF. ACOG states that first-trimester ultrasound is the most accurate method to establish or confirm gestational age.
Examples
| Example | Input | Expected result |
|---|---|---|
| Due date from New Year | |
EDD 2026-10-08, 280 calendar days after LMP |
| Twelve weeks | |
84 elapsed days, or gestational age 12 weeks 0 days |
| Leap year | |
EDD 2024-12-05 after adding 280 calendar days |
Limitations
- An LMP estimate, not a clinical EDD, and not a guarantee of the actual birth date
- No cycle-length adjustment; it may be inaccurate with irregular cycles, uncertain LMP or bleeding that was not a menstrual period
- Does not use intercourse, estimated conception, ultrasound, embryo-transfer or IVF dates
- Gestational-age calculation is limited from LMP through 42 weeks and does not assess medical risk or urgency
- Abnormal symptoms, bleeding, severe pain or an emergency require medical services; do not decide care from this page
Frequently asked questions
Why is pregnancy counted from the last menstrual period?
By convention, gestational age starts on the first day of LMP and EDD is 280 days later. This includes roughly two pre-conception weeks in a typical cycle within the gestational-age count.
Can ultrasound change the due date?
A clinician compares LMP dating with ultrasound and other information. ACOG identifies first-trimester ultrasound as the most accurate way to establish or confirm gestational age; selection and documentation of the clinical EDD belong with the care team.
What if cycles are irregular or LMP is unknown?
This page's result may be unreliable. Tell the prenatal-care professional, who can use history, ultrasound and other clinical information for dating.
Can this be used after IVF or embryo transfer?
No. This page supports only LMP dating. Assisted-reproduction pregnancies use procedure-specific dates and information supplied by the clinic.
References
- ACOG — When Pregnancy Goes Past Your Due Date Verified 2026-08-04
- ACOG — Methods for Estimating the Due Date, Committee Opinion No. 700 Verified 2026-08-04
- ACOG — Prenatal Care Verified 2026-08-04
Content and calculation method last reviewed: