How is the expected date of delivery (EDD) calculated in Sri Lanka?

By Naegele's rule, the clinical standard reflected in the mother-held Pregnancy Record: EDD = first day of your last menstrual period (LMP) + 280 days (40 weeks). This calculator also adjusts for your cycle by adding (cycle length − 28) days, because a longer or shorter cycle shifts the day you ovulate.

What is POA (Period of Amenorrhoea) in a pregnancy record?

POA is how Sri Lankan clinics measure gestational age — the number of completed weeks and days since your last period, written like "28w 2d". Your PHM and clinic staff track everything in POA rather than months, so this tool shows POA directly to match your Pregnancy Record.

How many antenatal clinic visits are recommended in Sri Lanka?

Sri Lanka follows the WHO 2016 model of eight antenatal contacts — around 12, 20, 26, 30, 34, 36, 38, and 40 weeks — plus at least three home visits from your Public Health Midwife (PHM). The tool dates each contact from your LMP so you can plan around work and travel.

When should I register with the PHM and get the Pregnancy Record?

Register early — ideally by 12 weeks (the first antenatal contact). Your Public Health Midwife opens your mother-held Pregnancy Record (part of the CHDR) at registration, and early booking means earlier screening, iron and folic acid, and dating confirmation.

How do I adjust my due date if my cycle is not 28 days?

Enter your real average cycle length. The tool adds (cycle length − 28) days to the standard 280-day count. For a 35-day cycle it pushes the due date 7 days later; for a 21-day cycle it moves it 7 days earlier. This matches how ovulation timing changes with cycle length.

Is this pregnancy calculator accurate?

The date arithmetic is exact and cross-checked two ways (280-day count and conception + 266 days agree to the day). But LMP-based dating itself can be off by a week or more if your cycle is irregular or you're unsure of your last period. An early ultrasound (CRL) is the most accurate dating method — always confirm with your MOH clinic.

Does it work for IVF pregnancies or twins?

No. IVF and embryo-transfer pregnancies are dated from the transfer day, not the LMP, so this tool would be wrong for them. Twins and triplets also tend to arrive earlier than a single-baby EDD. For those cases, use the dating your fertility clinic or obstetrician gives you.

What does the trimester marker mean?

Trimesters follow the standard clinical split: first is 0–13w6d, second is 14w0d–27w6d, and third is 28w0d onward. Term (safe-to-deliver) is 37w0d–41w6d, and 42w0d or later is post-term, which your clinic monitors closely.

Sri Lanka · Health

Pregnancy Due Date & Antenatal Schedule Calculator — Sri Lanka

Enter your last period and cycle length to get your due date (EDD), how many weeks pregnant you are in POA, your trimester, and a dated Family Health Bureau antenatal clinic schedule. No signup, no ads, sources cited below.

By Induwara Ashinsana— Executive Director, Ryzera TechnologiesUpdated Jul 18, 2026

Your pregnancy timeline

First day of your last period (LMP)

The first day of your most recent menstrual period.

Average cycle length (days)

Whole number, 20–45 days. Leave at 28 if unsure.

Common cycles

Show my progress as of

Defaults to today. Change it to see where you were (or will be) on any date.

Enter your last period date to begin.

You'll get your due date, how many weeks along you are (POA), your trimester, and a dated antenatal clinic schedule.

This is a guide, not medical advice. Confirm your dating with your MOH clinic, PHM, or an ultrasound scan. LMP-based dates can be off by a week or more if your cycle is irregular.

Sources: WHO 2016 antenatal care model & Sri Lanka Family Health Bureau — cited in full below the calculator.

How it works

The calculator uses only calendar-date arithmetic — no data is fetched or uploaded. Everything follows the dating method printed in the mother-held Pregnancy Record and the antenatal contact schedule Sri Lanka's Family Health Bureau (FHB) adopted from the World Health Organization's 2016 model. There are five steps.

Due date (Naegele's rule, cycle-adjusted). EDD = LMP + 280 days + (cycle − 28). The 280 days is 40 weeks and assumes a 28-day cycle with ovulation on day 14. A longer or shorter cycle moves ovulation, so we shift the due date by (cycle length − 28) days.
Period of Amenorrhoea (POA). totalDays = asOf − LMP, then weeks = ⌊totalDays ÷ 7⌋ and days = totalDays mod 7, shown as Xw Yd — the exact format your clinic and PHM use.
Trimester. First is 0w0d–13w6d, second is 14w0d–27w6d, third is 28w0d onward. The full-term window is 37w0d–41w6d; 42w0d or later is post-term.
Estimated conception. conception = LMP + (cycle − 14), the ovulation estimate. For a 28-day cycle this is the due date minus 266 days.
Antenatal contact dates. For each WHO/FHB recommended week (12, 20, 26, 30, 34, 36, 38, 40) the date is LMP + week × 7. The first is a "register early with your PHM by 12 weeks" milestone.

The due date is verified two ways so you can trust it: the 280-day Naegele count and the "conception + 266 days" method are algebraically identical (both equal LMP + cycle length + 252 days) and always agree to the day. This is LMP-based dating only — it does not use ultrasound (CRL/BPD) measurements, IVF transfer dates, or multiple-pregnancy adjustments, which are your clinician's job.

Worked examples

Standard 28-day cycle

LMP = 1 Jan 2026, cycle = 28, as-of = 18 Jul 2026
EDD = 1 Jan + 280 + (28−28) = 8 Oct 2026 (Thursday)
POA = 18 Jul − 1 Jan = 198 days = 28w 2d → third trimester
Conception = 1 Jan + (28−14) = 15 Jan 2026
34-week clinic contact = 1 Jan + 238 = 27 Aug 2026

Long 35-day cycle (cycle adjustment)

LMP = 15 Mar 2026, cycle = 35, as-of = 18 Jul 2026
EDD = 15 Mar + 280 + (35−28) = 15 Mar + 287 = 27 Dec 2026
Cross-check: conception 5 Apr + 266 = 27 Dec 2026 ✓
POA = 18 Jul − 15 Mar = 125 days = 17w 6d → second trimester
Next contact at 20 weeks = 15 Mar + 140 = 2 Aug 2026

Short 21-day cycle (edge case)

LMP = 1 Jun 2026, cycle = 21, as-of = 18 Jul 2026
EDD = 1 Jun + 280 + (21−28) = 1 Jun + 273 = 1 Mar 2027
Conception = 1 Jun + (21−14) = 8 Jun 2026
POA = 18 Jul − 1 Jun = 47 days = 6w 5d → first trimester
First contact due by 12 weeks = 1 Jun + 84 = 24 Aug 2026

Frequently asked questions

Sources & references

Naegele's rule (LMP + 280 days) is the universal obstetric dating standard reflected in the FHB Pregnancy Record. These sources were last cross-checked on 2026-07-18. This tool is a guide, not medical advice — confirm your dating with your MOH clinic, PHM, or an ultrasound scan.

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