Pregnancy
Pregnancy calculators for due date estimates, gestational age, and pregnancy date conversions — with formulas, worked examples, and FAQs.
Pregnancy Due Date Calculator
Calculate estimated due date (EDD) from last menstrual period or conception date
Gestational Age Calculator
Calculate current gestational age from LMP or ultrasound dating
How Pregnancy Calculations Work
Pregnancy date calculations often start from LMP (last menstrual period) or a known gestational age at a specific date. These reference points help establish when the pregnancy began and when the baby is expected to arrive.
Calculators convert between dates, weeks+days, and estimated due date (EDD). Importantly, clinical dating may use ultrasound or medical documentation, so always confirm which dating method your service uses.
Common Pregnancy Calculations Explained
Estimated due date (EDD) from LMP
A common estimate uses the first day of the last menstrual period (LMP) and adds a standard pregnancy length.
Example question:
LMP (first day) is 1 March 2025. What is the estimated due date (EDD) using the 280-day method?
(Equivalent: +40 weeks)
Worked example:
Result: Answer: EDD = LMP + 40 weeks (calculator provides exact date).
Tip: Always confirm whether dating is based on LMP or ultrasound.
Gestational age from LMP (weeks + days)
Gestational age is the time elapsed since LMP, usually expressed as weeks + days.
Example question:
LMP is 1 March 2025. Today's date is 15 April 2025. What is the gestational age?
Weeks = floor(days ÷ 7)
Days = remainder
Worked example:
Result: Answer: Gestational age = X weeks + Y days (calculator provides exact).
Tip: Use weeks + days, not decimal weeks.
Date conversion: add weeks/days to a date
This is used to work forward from a known gestation point (e.g., "12+3 on this date") to another date.
Example question:
A pregnancy is 12 weeks + 3 days on 10 May 2025. What date will it be at 20 weeks?
Convert gestational difference to days:
Δdays = (Δweeks × 7) + Δextra_days
Worked example:
Result: Answer: Target date = known date + 53 days (calculator provides exact).
Tip: Convert GA differences to days, then add to the calendar date.
When These Calculators Are Used
- •Estimating EDD from LMP (quick reference)
- •Converting dates into gestational age (weeks + days)
- •Planning timelines by adding weeks/days to a known date
- •Cross-checking documentation consistency (dates vs weeks)
- •Education/study and quick admin calculations
Clinical safety note:
Pregnancy dating can differ depending on LMP accuracy and ultrasound/medical documentation. Always follow local protocols and documented dating methods. These calculators support calculation checking but do not replace clinical judgement. Examples on this page are for calculation practice only.
Related Calculator Categories
Frequently Asked Questions
Always confirm which dating method your service uses.