WWorkmate

Due Date Calculator

Enter your last period to instantly see the due date, current pregnancy weeks, trimester, and days to go.

Due date

Estimated due date
2027-04-07

Days to go 253 days · Progress 9.6%

Current pregnancy
3weeks 6days
Trimester
1

Based on Naegele's rule (LMP + 280 days). Cycles other than 28 are auto-adjusted. The actual date is confirmed by ultrasound; term spans 37-42 weeks so the due date is an estimate.

What this tool does

The due date calculator estimates your delivery date from the last menstrual period (LMP). Based on Naegele's rule (LMP + 280 days), it shows the current pregnancy week, trimester, progress, and days to go, and auto-adjusts for cycles other than 28 days.

Who uses this

  • Calculate the due date after confirming pregnancy
  • Check current pregnancy week and trimester
  • Plan prenatal checkups and maternity leave
  • Adjusted due date for irregular cycles
  • Track pregnancy progress and D-day

How to use

  1. 1Enter the first day of your last menstrual period (LMP).
  2. 2Enter your average cycle length. Default is 28 days; otherwise ovulation timing is adjusted.
  3. 3See the due date, current week/trimester, progress, and days remaining.

Naegele's rule

EDD = LMP + 280 days (40 weeks) = LMP + 1 year − 3 months + 7 days Pregnancy weeks = (today − LMP) / 7 Trimester: 1st 0-13 wks, 2nd 14-27, 3rd 28+ Cycle adjustment: shift EDD by (cycle − 28) days e.g. 35-day cycle → EDD 7 days later

Real examples

Example 1: LMP Jan 1 (28-day cycle)

Jan 1 + 280 days = Oct 8 due date. Based on the 40-week full term.

Example 2: 20 weeks pregnant

140 days after LMP = 20 weeks = 2nd trimester. Anatomy scan and sex determination period. 50% progress.

Example 3: 35-day cycle

Later ovulation shifts the due date 7 days past the 28-day estimate. Cycle adjustment gives a more accurate date.

Pregnancy & childbirth in Korea — checklist for foreign residents

After confirming pregnancy

  • Register your pregnancy with the local public health center (보건소), online via e-보건소 (e-health.go.kr), using your Alien Registration Number.
  • Registered expectant mothers receive free prenatal screening tests at the health center.
  • Apply for the National Happiness Card (국민행복카드) pregnancy/childbirth voucher: ₩1,000,000 single / ₩1,400,000 multiples.
  • The voucher is available to foreigners who are National Health Insurance subscribers or dependents with valid alien registration (verify your NHI status).

Prenatal care & choosing a hospital

  • Choose an OB/GYN clinic or a hospital with a delivery unit; many foreigners prefer one with interpretation services.
  • Follow the standard prenatal checkup schedule and use voucher funds toward checkups and delivery.
  • Keep your NHI coverage active throughout pregnancy so delivery is covered as an insured benefit.
  • Confirm your hospital can issue the birth documents you'll need for both Korean and home-country registration.

After birth — registration, ARC & insurance

  • File the birth report at the district community center (주민센터) within 1 month of birth.
  • If one parent is Korean, the child may acquire Korean nationality; if BOTH parents are foreign, the child does NOT automatically get it (verify).
  • Foreign-national babies must also be registered with the home-country embassy/consulate (passport).
  • If both parents are foreign, get the baby's passport, then apply for residence status / ARC at immigration before staying over 90 days (verify requirements).
  • Register the baby as a dependent on a parent's National Health Insurance so medical and vaccination costs are covered.

Cash benefits — foreigner eligibility (verify each)

  • First-Meet Voucher (첫만남이용권, ₩2M first child / ₩3M second+): requires the child to have a Korean resident-registration number; foreign-national children are generally NOT eligible (verify).
  • Child Allowance (아동수당, ₩100,000/month under age 8): paid based on the CHILD's nationality — generally only if the child holds Korean nationality (verify).
  • Apply for child allowance within 60 days of birth to receive it retroactively to the birth date.
  • These benefits are suspended if the child stays abroad for 90+ days.
  • Eligibility varies by residence status and the child's nationality — confirm at the community center, Bokjiro (bokjiro.go.kr), or ☎129.

Frequently asked questions

Will I deliver exactly on the due date?

It's an estimate. Full term spans 37-42 weeks, and only ~5% deliver on the exact due date. Most deliver within ±2 weeks.

Is it accurate with irregular cycles?

Naegele's rule assumes a regular 28-day cycle. Irregular cycles increase error, so an ultrasound (fetal-size) due date is more accurate. This tool supports cycle adjustment but is for reference.

When does pregnancy week counting start?

The first day of LMP is week 0 day 0. Actual conception is ~2 weeks later, but since exact ovulation is unknown, LMP is the standard. So 'week 4' is around the expected period date.

How are trimesters divided?

1st 0-13 weeks (organ formation, nausea), 2nd 14-27 (stable, movement), 3rd 28+ (rapid growth, term prep). Each has different tests and precautions.

It differs from the ultrasound date — which is right?

The early ultrasound (7-12 weeks) date is most accurate. If it differs from LMP by 1+ weeks, the ultrasound date is usually adopted. This tool estimates from LMP, so prioritize your OB-GYN's confirmed date.

Same due date for twins?

Twins/multiples tend to be born earlier (usually before 37 weeks). This calculator assumes a singleton, so follow medical guidance for multiples.

Cautions

  • •Naegele's rule (LMP+280) estimate — ultrasound date is more accurate.
  • •Full term spans 37-42 weeks; ~5% deliver on the due date.
  • •Irregular cycles increase error.
  • •Twins/multiples tend to be earlier (separate).
  • •Confirm the exact date via OB-GYN ultrasound.

Last reviewed: 2026-05-30

Due Date Calculator — pregnancy weeks & trimester