Frequently Asked Questions

Naegele's rule is the most standard method for calculating a due date, established by the 19th-century German obstetrician Franz Karl Naegele. It is used by obstetricians worldwide.

Calculation

Reference point: the first day of the last menstrual period (LMP)

Due date = LMP + 280 days = LMP + 40 weeks

On the calendar: take the LMP, subtract 3 months and add 7 days.

Why 280 days?

It comes from the statistical observation that an average pregnancy lasts about 40 weeks (280 days). The 280 days assume:

• A menstrual cycle of 28 days (the average)
• Ovulation occurring 14 days after the start of the period
• Fertilization happening shortly after ovulation
• Actual pregnancy duration of about 266 days from conception

Counting from the LMP is practical because the start of the last period is usually remembered, while the exact day of ovulation or conception is not.

How accurate is it?

Only about 5% of births occur exactly on the EDD. Statistically:

• Within ±1 week of EDD: about 65%
• Within ±2 weeks of EDD: about 90%
• Normal delivery range: 37–42 weeks of pregnancy

So Naegele's rule is not an exact date but an estimate of "around when labor is likely".

What are the limitations?

The estimate is less accurate when:

• The menstrual cycle is not 28 days (longer cycles shift the EDD later)
• The LMP is not remembered precisely
• Pregnancy was achieved through IVF or other assisted reproduction — the embryo transfer date is more accurate
• Variables such as maternal age, ethnicity, and number of previous pregnancies

How is it different at a clinic?

Obstetricians combine Naegele's rule with ultrasound measurements. In early pregnancy (8–13 weeks), the fetus's crown-rump length (CRL) is strongly correlated with gestational age, which allows for a more accurate EDD.

Therefore, if your doctor's EDD differs from this calculator, trust your doctor's date.

About this calculator

Our due date calculator uses the pure Naegele's rule (LMP + 280 days, 28-day cycle assumed). Cycle-length input will be added in a future update.

This site uses the 14-day luteal phase assumption. From an LMP, conception ≈ LMP + (cycle - 14); from a due date, conception ≈ EDD - 266 days (= 280 - 14); from current gestational age, conception ≈ measurement date - gestational days + 14.

"Conception" medically refers to the moment sperm fertilizes the egg. Because sperm can survive up to 5 days inside the body, fertilization may actually occur anywhere within ±5 days of the estimated ovulation. The calculator therefore shows both a single estimate and a likely range.

The exact conception date can only be confirmed by an early ultrasound (typically between 6 and 10 weeks of pregnancy). This calculator is a statistical estimate, for reference only.

The IVF (in vitro fertilization) due date is calculated from two inputs: the embryo transfer date and the embryo day at transfer. This follows the SART (Society for Assisted Reproductive Technology) and ASRM (American Society for Reproductive Medicine) standards.

Formula

• Day 5 blastocyst transfer: EDD = transfer date + 263 days
• Day 3 cleavage transfer: EDD = transfer date + 261 days
• Day 6 delayed blastocyst transfer: EDD = transfer date + 262 days

Why this differs from the standard due date

Naturally conceived pregnancies use LMP + 280 days (Naegele's rule), but IVF has a precisely known fertilization timeline, so anchoring to the transfer date is more accurate. For Day 5 transfers, transfer + 263 days lands on the same EDD as LMP + 280 days.

Notes

• Actual delivery may vary by about ±2 weeks around the EDD.
• If your obstetrician has given you an ultrasound-based EDD, that value takes priority.
• This calculator provides estimates for reference only — it is not a medical diagnosis.

This site assumes a 14-day luteal phase. Ovulation is estimated as next period minus 14 days, and the fertile window covers 5 days before to 1 day after ovulation — a 7-day window.

Sperm can survive up to 5 days, so intercourse a few days before ovulation may also result in pregnancy. However, the 14-day luteal phase is a statistical average; actual length varies from 8 to 16 days.

For more accurate ovulation tracking, combine this estimate with basal body temperature (BBT), LH ovulation tests, and cervical mucus observation.

This site uses LMS tables from the WHO 2006 Child Growth Standards. For each sex and age in days, an L, M, S triple yields a standardized Z-score and percentile.

Formula

Z = ((X / M)^L − 1) / (L · S) (L ≠ 0)
Z = ln(X / M) / S (L = 0)
Percentile = Φ(Z) × 100 (normal CDF)

X = measurement value, L·M·S = reference parameters by sex and age.

Supported range

• Age — 0–60 months (0–1856 days)
• Metrics — Weight, height/length, head circumference
• Standards — WHO 2006 (designed to be ethnicity-neutral)

Reading percentiles

• 50 — Middle of peers
• 3 to 97 — Statistical normal range
• Below 3 / above 97 — May warrant monitoring (individual trend matters more than one point)

Percentiles describe population distribution, not individual health. A child's own trend over time is more informative than a single value; for clinical assessment, see a pediatrician.

Based on the U.S. National Academy of Medicine (NAM, formerly IOM) 2009 pregnancy weight gain guidelines.

Recommended range by pre-pregnancy BMI (singleton)

• Underweight (BMI < 18.5): 12.5–18 kg
• Normal (18.5–24.9): 11.5–16 kg
• Overweight (25–29.9): 7–11.5 kg
• Obese (≥ 30): 5–9 kg

Weekly rate (2nd–3rd trimester)

• Underweight: 0.44–0.58 kg/week
• Normal: 0.35–0.50 kg/week
• Overweight: 0.23–0.33 kg/week
• Obese: 0.17–0.27 kg/week

First-trimester gain is typically 0.5–2 kg.

Twin pregnancy

• Normal BMI: 16.8–24.5 kg
• Overweight: 14.1–22.7 kg
• Obese: 11.3–19.1 kg

Notes

• This calculator displays the NAM recommended range and is not a medical prescription.
• Gestational diabetes, gestational hypertension, multifetal, and adolescent pregnancy require individualized obstetric assessment.
• The weekly trend matters more than a single point measurement.

This site uses the Hadlock-4 formula published by Dr. Hadlock in 1985.

Formula

log₁₀(EFW) = 1.3596 − 0.00386·AC·FL + 0.0064·HC + 0.00061·BPD·AC + 0.0424·AC + 0.174·FL

EFW in grams; inputs in cm.

Four measurements

• BPD (Biparietal Diameter) — skull width between the parietal bones
• HC (Head Circumference)
• AC (Abdominal Circumference)
• FL (Femur Length)

Accuracy and limits

• ±10–15% error vs actual birth weight
• Error grows in late pregnancy
• At extremes (macrosomia, low birth weight) other formulas (Shepard, Hadlock 1/2/3) may fit better
• Use all four values from the same scan date

If your hospital's estimate differs from this calculator, the hospital takes priority.

Recommended storage times per the US CDC breast milk storage guidelines (for freshly expressed milk).

• Room temperature (≤ 25°C / 77°F): 4 hours
• Refrigerator (≤ 4°C / 39°F): 4 days
• Freezer (≤ -18°C / 0°F): 6 months (best), up to 12 months
• Thawed in refrigerator: 24 hours, do not refreeze

This calculator uses the recommended limits. Milk is safe up to 12 months in the freezer but nutritional quality drops, so try to use it within 6 months.

Note: Discard immediately if color or smell is off. For newborns and preemies, use shorter windows than the guideline.

This site estimates the recommended testing time based on Wilcox NEJM 1999. From your estimated conception date (last intercourse or ovulation):

• Blood hCG test: ~11 days later
• Urine pregnancy test: ~14 days later

Blood hCG is a quantitative test at a clinic — earliest and most accurate. Some detection is possible from day 9–10 after conception, but stable positive results require 11+ days.

Urine pregnancy tests are home strips from a pharmacy. They are generally reliable around the missed period (about 14 days post-conception). Testing too early can produce false negatives.

Ovulation and implantation timing vary by ±2–3 days per person, so retest after 1–2 weeks if negative. For confirmation, see an obstetrician.

Implantation is when the fertilized embryo embeds into the uterine lining after ovulation. Based on Wilcox et al. 1999 NEJM.

Implantation timing (days post-ovulation)

• Day 6–7: very rare
• Day 8: ~18%
• Day 9: ~36% (most common)
• Day 10: ~30%
• Day 11: ~11%
• Day 12+: late implantation — increased miscarriage risk

Symptoms

• Implantation bleeding — light spotting in ~25% of women
• Implantation cramps — mild abdominal tugging, not universal
• No symptoms is also normal

When you can test

• After implantation, βhCG starts and doubles every 24–48 hours
• Home urine test: from 12–14 days post-ovulation (around the expected period)
• Testing too early → false negative. 1–2 days after a missed period is more accurate
• Serum βhCG: positive earlier (9–11 days post-ovulation)

This calculator marks average windows as a reference; definitive diagnosis requires obstetric evaluation.

Emergency contraception reduces the chance of pregnancy after unprotected sex or contraceptive failure.

Options and recommended windows

Per WHO and FDA, there are three options with different windows.

• Levonorgestrel — within 72 hours (3 days)
• Ulipristal acetate — within 120 hours (5 days)
• Copper intrauterine device insertion — within 120 hours (5 days)

All options are more effective the sooner they are used.

What this calculator does

It shows objectively how much of each recommended window remains from the time you enter; it does not estimate effectiveness or recommend a specific option.

Talk to a professional

Prescription rules and availability differ by country. The right choice given your weight, other medications and health is for a pharmacist or doctor to decide. Contact a pharmacy, OB-GYN or public health clinic as soon as possible.

A fetal kick count is a way to monitor fetal well-being by counting movements over a set time. Based on ACOG Practice Bulletin #229 (2021) and the British Cardiff 'Count to 10' method.

When to start

• High-risk pregnancy: daily from 28 weeks
• Normal pregnancy: typically 28 weeks, by 36 weeks at the latest

Cardiff 'Count to 10' method

• After a meal, lie on your side (left preferred)
• Kicks, rolls, and stretches all count as one
• Time how long until 10 movements — typically under 2 hours

Contact obstetrician immediately if

• Fewer than 10 in 2 hours
• Significant decrease from baseline
• No movement at all

Decreased movement can be an early sign of IUGR, low amniotic fluid, gestational hypertension, or rarely stillbirth — the golden window matters.

Notes

• This calculator records time and counts and does not replace medical evaluation.
• Decisions are guided primarily by your obstetrician's instructions.

βhCG (beta human chorionic gonadotropin) is the pregnancy hormone produced by the placenta after implantation. Before about week 6, βhCG typically doubles every 48–72 hours, and this doubling time is a reference indicator of whether the pregnancy is progressing as expected.

Formula

doubling time = ΔT × ln2 / ln(v2/v1)

ΔT = hours between draws, v1 / v2 = first and second values (mIU/mL).

Reference range

• Before 6 weeks: about 48–72 hours
• After 6 weeks: gradually slows beyond 96 hours
• Peaks around week 10 and then declines

Sources: ACOG and Endocrine Society guidelines.

How to interpret

• Outside the range can still be a healthy pregnancy, and in range does not rule out a problem.
• Ectopic pregnancy, miscarriage and similar conditions are diagnosed by an obstetrician using ultrasound and the full clinical picture.
• Timestamp accuracy and lab-to-lab assay differences add uncertainty.

This calculator is not a diagnostic tool. If you are concerned, contact your obstetrician promptly.

Based on the American Academy of Pediatrics (AAP) and WHO infant feeding guidance.

Daily formula by age

• 1–6 months: about 150 ml/kg/day
• 6–12 months: about 120 ml/kg/day (combined with solids)

Example: a 5 kg newborn needs about 750 ml/day, an 8 kg 6-month-old about 960 ml/day.

Feedings per day

Newborns feed roughly 7–8 times a day, decreasing to 4–5 after 6 months. Per-feed amount = daily total ÷ feedings per day.

Notes

• This is a recommended estimate, not a medical prescription.
• Preterm, low-birth-weight, milk-protein allergy, reflux or poor weight gain → follow your pediatrician first.
• Appetite varies. A ±10–20% difference is normal.

The WHO recommends starting complementary foods at 6 months (180 days). The AAP allows starting between 4–6 months based on developmental readiness.

4 stages by region

• Korea (Ministry of Health / Korean Pediatric Society): early 4–6m · mid 7–8m · late 9–11m · complete 12–15m
• Japan (MHLW 2019): gokkun 5–6m · mogu-mogu 7–8m · kami-kami 9–11m · paku-paku 12–18m
• WHO/AAP: start at 6m; stage transitions based on developmental signs

Allergen introduction

The LEAP (2015) and EAT (2016) studies show that early introduction of peanut and egg at 4–6 months reduces allergy risk. Start one at a time in small amounts; consult a pediatrician first if there is a family history.

Readiness signs

• Holds head steady
• Sits with support
• Shows interest in food, opens mouth
• Tongue-thrust reflex has diminished

Cautions

• No honey before 12 months (botulism risk)
• No whole nuts — use powder or nut butter
• This calculator is a reference; for preterm, developmental delay, or family allergy history, consult a pediatrician first

An interval is the time from the start of one contraction to the start of the next; a duration is how long one contraction lasts.

5-1-1 rule (ACOG general guidance)

• 5 minutes apart or less
• 1 minute long or more
• Sustained for at least 1 hour

Meeting all three is a typical cue to head to the hospital.

Caveats

• First-time vs subsequent labor, distance to the hospital, and complications can shift the right time.
• If your water breaks, you see bright red bleeding, or fetal movement drops, call your provider even before 5-1-1.
• Entries are kept only in your browser (localStorage) and are never transmitted.

Your OB-GYN's instructions take priority.

The Apgar score is a newborn vitality indicator devised by Dr. Virginia Apgar (Columbia anesthesiology) in 1952. At 1 and 5 minutes (and 10 minutes if needed) after birth, five components are each scored 0, 1, or 2 for a total from 0 to 10.

Five components (APGAR mnemonic)

• Appearance — skin color
• Pulse — heart rate
• Grimace — reflex response
• Activity — muscle tone
• Respiration — breathing effort

Reference ranges (AAP/ACOG 2015, reaffirmed 2021)

• 7–10 — reassuring
• 4–6 — moderately abnormal (consider stimulation or supplemental oxygen)
• 0–3 — immediate resuscitative care indicated

Important caveat

The AAP/ACOG statement makes clear that the score is only an immediate indicator and does not determine long-term neurodevelopmental outcomes. This calculator is for delivery-room documentation and reference; actual evaluation and care follow the delivery-room team's judgment.

Based on the American Academy of Pediatrics (AAP) 2016 consensus statement on sleep duration and pediatric wake-window guidance.

Total daily sleep by age

• 0–3 months: 14–17 hours
• 4–11 months: 12–16 hours
• 12–24 months: 11–14 hours

Wake window by age

• 0–1 months: 45–60 min / 5–7 naps
• 2–3 months: 1–1.5 h / 4–5 naps
• 4–5 months: 1.5–2 h / 3–4 naps
• 6–8 months: 2–3 h / 2–3 naps
• 9–11 months: 3–4 h / 2 naps
• 12–17 months: 4–5 h / 1–2 naps
• 18–24 months: 5–6 h / 1 nap

Estimating the next nap

Next nap = last wake time + average wake window.

Notes

• These are reference estimates. Individual variation is wide.
• Watch for sleep cues — eye-rubbing, yawning, zoning out.
• Breathing difficulty, sleep apnea or heavy snoring → see a pediatrician first.

Estimated next nap time = "last wake time + average wake window for the baby's age".

Worked example

If your 5-month-old's wake window is 105–135 minutes, start watching for sleep cues about 2 hours (the mid-range) after the last wake.

How to read the displayed time

• It is not a command to put the baby down at that exact minute.
• It is a window during which to start watching for cues.
• Cues earlier → start the nap earlier; cues later → a few more minutes of awake time is fine.

Sleep cues

• Eye-rubbing or ear-tugging
• Frequent yawning
• Glazed stare into space
• Fussing at small triggers
• Slowed movement

Notes

• Wake windows are averages, not a formula (AAP / Pediatrics 2016; Polly Moore; Marc Weissbluth). A ±30-minute spread is common.
• During the 4-month sleep regression the wake window may suddenly lengthen or shorten.
• Missing cues can lead to an overtired state that makes falling asleep harder.
• For breathing difficulty, sleep apnea or heavy snoring → see a pediatrician first.

Baby teeth usually start erupting between 6–10 months with the lower central incisor (front bottom), and all 20 teeth are typically complete by 25–33 months with the upper second molar.

AAPD (American Academy of Pediatric Dentistry) average eruption times:

• Lower central incisor: 6–10 months
• Upper central incisor: 8–12 months
• Lateral incisor: 9–16 months
• First molar: 13–19 months
• Canine: 16–23 months
• Second molar: 23–33 months

Individual variation is wide; ±6 months is still normal. If no tooth has appeared by 12 months, see a pediatric dentist.

Begin brushing as soon as the first tooth appears (AAP recommendation).