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Pregnancy Due Date Calculator

Estimate your pregnancy week and days remaining until your due date using Naegele's rule (LMP + 280 days). Adjusted for your menstrual cycle length.

Written by CalcVault Editorial Team
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Fill in the fields above and click Calculate to see your results.

How to use

Enter the length of your typical menstrual cycle and the number of days since your Last Menstrual Period (LMP). The calculator applies the Naegele's rule adjusted for cycle length to predict your estimated due date (EDD).

It also details how many weeks and days you have been pregnant, as well as the time remaining. This gives expecting parents in Vietnam a reliable timeline to prepare for their baby's arrival.

Keep in mind that this is only an estimate to help you plan. You should always consult with your healthcare provider for clinical tracking and ultrasound measurements to determine the most accurate due date and monitor the healthy development of your pregnancy.

How it's calculated

Cycle Adjustment (days)

cycle_length - 28

Days added or subtracted for cycles longer or shorter than 28 days

Days Pregnant

lmp_days_ago + adjusted_lmp_offset

Estimated number of days since conception (adjusted for cycle length)

Weeks Pregnant

floor(days_pregnant / 7)

Current week of pregnancy (Naegele's rule: LMP + 280 days = due date)

Days Until Due Date

max(0, 280 - days_pregnant)

Days remaining until estimated due date (40 weeks = 280 days from LMP)

Weeks Until Due Date

floor(days_remaining / 7)

Full weeks remaining until estimated due date

Examples

LMP 14 days ago, standard 28-day cycle

  • Menstrual Cycle Length:28
  • Days Since Last Menstrual Period (LMP):14

Result

  • Days Pregnant:14
  • Days Until Due Date:266
  • Weeks Pregnant:2
  • Weeks Until Due Date:38
  • Cycle Adjustment (days):0

With a standard 28-day cycle and 14 days since LMP, you are exactly 2 weeks pregnant. You have 38 weeks remaining until the due date. This calculation assumes ovulation happened right around day 14, placing you at the very beginning of the fetal development tracking period.

LMP 70 days ago, standard 28-day cycle

  • Menstrual Cycle Length:28
  • Days Since Last Menstrual Period (LMP):70

Result

  • Days Pregnant:70
  • Days Until Due Date:210
  • Weeks Pregnant:10
  • Weeks Until Due Date:30
  • Cycle Adjustment (days):0

At 70 days since your LMP on a standard 28-day cycle, you are exactly 10 weeks pregnant. There are 30 weeks remaining for fetal development. At this milestone, you are nearing the end of your first trimester, a critical period for your baby's organ formation.

Frequently Asked Questions

What is Naegele's rule?

Naegele's rule estimates the due date by adding 280 days (40 weeks) to the first day of the last menstrual period (LMP). It assumes a standard 28-day cycle. This calculator adjusts for longer or shorter cycles by shifting the estimate accordingly.

Why does cycle length affect the due date?

Naegele's rule assumes ovulation occurs on day 14 of a 28-day cycle. If your cycle is 35 days, ovulation likely occurs around day 21, meaning conception happened later — so the due date shifts forward by 7 days. The calculator adds (cycle_length - 28) days to account for this.

How accurate is this calculator?

This calculator provides an estimate based on Naegele's rule, which is the standard clinical method. However, actual due dates can vary by 2 weeks in either direction. An ultrasound scan in the first trimester provides a more accurate estimate. Always confirm your due date with a qualified healthcare provider.

How accurate is the estimated due date?

The due date is an estimate based on averages. Only about 4-5% of babies are born exactly on their estimated due date; most arrive safely somewhere between 37 and 42 weeks of pregnancy. Variations are completely normal and expected.
CalcVault Editorial Team

CalcVault Editorial Team

Verified Content Team

The CalcVault Editorial Team is a group of finance, health, and mathematics specialists dedicated to producing accurate, bilingual calculator content for Vietnamese and global small business owners. Every formula on CalcVault undergoes rigorous source verification against authoritative bodies including the IRS, CFPB, CDC, WHO, and NIST before publication. Our process includes independent peer review, structured fact-checking, and scheduled content audits to ensure every calculator remains up-to-date with the latest regulatory and scientific standards. We are committed to editorial independence from our advertising partners.

Areas of Expertise

Personal FinanceVietnam Tax & PayrollHealth Metrics & BMIApplied MathematicsBusiness LendingSMB Financial Planning
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