This EDD calculator gives you your Estimated Delivery Date — the date your baby is expected to arrive — using either your last menstrual period or your conception date.
EDD is one of the first and most important numbers in any pregnancy. It organises your entire prenatal care schedule, guides your OB-GYN’s clinical decisions, and gives you a clear timeline to prepare around. Enter your dates below and get your EDD instantly, along with how many days remain and your current pregnancy week.
What your EDD means:
Your Estimated Delivery Date is a calculated estimate — not a guaranteed date. Around 80% of babies are born within two weeks before or after the EDD. Only about 5% arrive exactly on the date. A baby born anywhere between 37 and 42 weeks is considered full term.
Your EDD stays the same throughout your pregnancy. It does not change as weeks pass. What changes is how many days remain until that date — and the progress your pregnancy makes toward it.
What is EDD in pregnancy — and why does it matter?
EDD stands for Estimated Delivery Date. It is also called the Estimated Due Date or Expected Date of Delivery — all three terms refer to the same thing: the date around which your baby is most likely to be born.
Your EDD is the cornerstone of your entire prenatal care plan. Every prenatal check-up schedule, every developmental milestone reference, every recommendation about tests, scans, and interventions is timed relative to your EDD and your gestational age at the time.
In the Philippines, your EDD appears on your maternity record card from your very first prenatal visit. Your OB-GYN and midwife use it to determine when to schedule your anatomy scan, when to begin weekly check-ups, when to discuss birth preferences, and when a delivery might be considered preterm, full term, or post-term.
Understanding your EDD also helps you plan practically — arranging maternity leave, preparing your hospital bag, planning for support at home after delivery, and knowing when to be alert for early labour signs.
EDD calculation formula — the two methods explained
There are two established formulas for calculating your EDD, depending on which date you know more reliably.
H3: EDD from LMP — Naegele's Rule
The most widely used method for how to calculate EDD in pregnancy is based on your Last Menstrual Period date, using a formula called Naegele's Rule:
EDD = LMP date + 280 days
280 days equals 40 weeks — the standard length of a full-term pregnancy counted from the first day of the last menstrual period. This formula was developed in the 19th century and remains the global clinical standard for EDD calculation, including in the Philippines.
The reason EDD is calculated from LMP rather than conception is practical. Most women know the first day of their last period far more reliably than they know when conception occurred. Conception typically happens around 14 days after the LMP in a standard 28-day cycle, and that offset is already built into the 280-day calculation.
Example: LMP of January 1 gives an EDD of October 8. LMP of July 15 gives an EDD of April 20 of the following year.
EDD from conception date
If you know your approximate conception date — for example, from tracking ovulation, using ovulation predictor kits, or through IVF where the date of fertilisation or transfer is precisely known — you can calculate your EDD using:
EDD = Conception date + 266 days
266 days equals 38 weeks from conception. Because conception typically occurs around 14 days after the LMP, this formula gives the same result as the LMP method when cycles are regular.
For IVF pregnancies, the transfer date is used with a specific adjustment depending on whether the embryo was a day 3 or day 5 transfer. Day 3 transfer: add 263 days. Day 5 transfer: add 261 days. Your fertility specialist will calculate this for you, but our calculator gives you a close estimate using the conception date method.
EDD formula for irregular periods
For women with irregular menstrual cycles — cycles that are consistently longer or shorter than 28 days — the standard LMP formula may not be accurate because it assumes a 28-day cycle with ovulation on day 14.
The adjusted formula for irregular cycles is:
EDD = LMP + 280 + (your average cycle length - 28)
Example: a 32-day cycle gives EDD = LMP + 284. A 24-day cycle gives EDD = LMP + 276.
This adjustment accounts for the fact that ovulation — and therefore conception — happens earlier in shorter cycles and later in longer cycles, shifting the EDD accordingly.
However, for women with irregular cycles, the most accurate EDD comes from an early first-trimester ultrasound rather than any formula-based calculation. The ultrasound measures the actual size of the embryo and gives a gestational age that is not affected by cycle length variation.
How to calculate EDD from LMP manually — step by step
If you want to know how to calculate EDD manually without a calculator, here is the step-by-step process:
Step 1: Write down the first day of your last menstrual period.
Step 2: Add 7 days to that date.
Step 3: Add 9 months to the result.
This is the simplified version of Naegele's Rule. The mathematical result is the same as adding 280 days, but working with months and days is sometimes easier than adding 280 to a date on a calendar.
Example using January 1:
January 1 + 7 days = January 8. January 8 + 9 months = October 8. EDD = October 8. This matches the result of January 1 + 280 days exactly.
Note: when adding 9 months crosses a year boundary, account for that. If your LMP is May 15, adding 7 days gives May 22. Adding 9 months to May 22 gives February 22 of the following year.
Our EDD calculator does all of this automatically. But knowing the manual method helps you understand and verify your result.
How to calculate EDD for irregular periods
Irregular periods create a real challenge for EDD calculation because the formula assumes consistent ovulation at day 14 of a 28-day cycle. When your cycle is shorter or longer, or varies significantly in length, your actual ovulation date — and therefore your conception date — shifts.
There are three practical approaches for calculating EDD with irregular periods:
The adjusted LMP formula — if you know your average cycle length (even approximately), use EDD = LMP + 280 + (your cycle length - 28). This gives a rough adjustment for cycles that differ from the 28-day standard.
Use ovulation tracking data — if you were using ovulation predictor kits, basal body temperature charting, or fertility monitoring when you conceived, you may have a more reliable estimate of your actual ovulation date. Use EDD = ovulation date + 266 days for a more accurate result.
Early ultrasound dating — this is the most reliable method for women with irregular cycles. An ultrasound performed between 7 and 12 weeks measures the size of the embryo directly and gives a gestational age estimate that is not affected by cycle irregularity. An ultrasound-derived EDD at this stage is accurate to within about five days.
If your period is irregular and you are trying to determine your EDD, the combination of an approximate LMP-based calculation and early ultrasound confirmation gives you the most useful and accurate result.
EDD calculator based on LMP versus conception date — which to use
The choice between the LMP method and the conception date method depends on which date you know more precisely.
For most women, the LMP date is the more reliable starting point. Period dates are tracked, noted, or remembered in a way that conception dates simply are not. Even women who were not actively trying to conceive often know roughly when their last period started.
The conception date method is more useful for women who were actively tracking their cycle, using ovulation tests, or undergoing fertility treatments where the timing of fertilisation is precisely known. In these cases, the conception date is actually the more accurate input.
For natural conception with a regular cycle, both methods give essentially the same EDD — because the LMP formula already assumes conception happened 14 days after the period started.
For IVF, the conception date (or transfer date) is the more precise method, and your fertility specialist will typically provide you with an EDD calculated from the transfer date rather than asking for your LMP.
EDD in Philippine prenatal care — what to expect
In the Philippines, your EDD is established at your first prenatal visit and recorded on your maternity record card. It is used throughout your pregnancy as the reference point for clinical decisions.
The Philippine Department of Health recommends a minimum of eight prenatal visits spaced relative to your gestational age — which is itself calculated from your EDD. Understanding your own EDD gives you a clear framework for when those visits should occur and what happens at each stage.
At around 18 to 20 weeks, your anatomy scan ultrasound is typically scheduled. This scan confirms that your baby's development matches the expected stage for your EDD, and may result in a slight EDD adjustment if there is a meaningful difference between the ultrasound measurements and the LMP-based calculation.
Between 36 and 40 weeks, your OB-GYN will assess cervical readiness and fetal position in preparation for delivery. Some providers in the Philippines recommend induction of labour if delivery has not begun by 41 weeks, depending on clinical findings and the mother's health.
If you are delivering at a government hospital, your EDD will be calculated and recorded by the attending midwife or OB-GYN at your first booking visit. PhilHealth-accredited facilities use standardised maternity records that include EDD as a primary field.
What happens if delivery does not occur on the EDD
The EDD is an estimate — and the large majority of deliveries do not happen exactly on that date. This is completely normal and expected.
Approximately 80% of babies are born within two weeks before or after the EDD. Only about 5% are born exactly on their estimated delivery date. The remaining deliveries are spread across the weeks around the EDD, with the most common birth week being week 39.
A baby born before 37 completed weeks is considered preterm. A baby born at 37 to 42 weeks is full term. Delivery after 42 weeks is considered post-term, and most OB-GYNs in the Philippines will recommend induction or closer monitoring at this stage.
If your EDD passes without delivery, your OB-GYN will typically increase monitoring — more frequent check-ups, non-stress tests to confirm fetal wellbeing, and assessment of amniotic fluid levels. These are precautionary measures, not signs that something is wrong.
Frequently asked questions
How do I calculate my EDD from my LMP?
Add 280 days to the first day of your last menstrual period. This gives your Estimated Delivery Date using Naegele's Rule — the standard clinical formula.
You can also use the simplified approach: add 7 days to your LMP date, then add 9 months. Both give the same result.
Our EDD calculator does this automatically. Enter your LMP date and your EDD appears instantly, along with days remaining and your current pregnancy week.
How do I calculate EDD manually?
Take the first day of your last menstrual period. Add 7 days. Then add 9 months to that date. The result is your estimated delivery date.
Example: LMP July 1. Add 7 days = July 8. Add 9 months = April 8 of the following year. EDD = April 8.
This manual method gives the same result as adding 280 days and works for women with regular 28-day cycles. For irregular cycles, an adjusted calculation or early ultrasound gives a more accurate EDD.
What is the EDD formula?
The standard EDD formula is Naegele's Rule: EDD = LMP + 280 days. For conception-based calculation: EDD = conception date + 266 days. For irregular cycles: EDD = LMP + 280 + (cycle length - 28).
All three methods aim to estimate the same date — 40 weeks from the LMP or 38 weeks from conception — adjusted for individual cycle variation where applicable.
How accurate is an EDD calculator?
An EDD calculator based on LMP is accurate within one to two weeks for women with regular 28-day cycles. For women with irregular cycles or uncertain LMP dates, accuracy decreases.
An early first-trimester ultrasound gives an EDD accurate to within about five days — more precise than any formula-based calculation. If your ultrasound EDD differs from your LMP-based EDD by more than five to seven days, your OB-GYN may update your EDD to reflect the ultrasound measurement.
Can my EDD change during pregnancy?
Your calculated EDD does not change. However, your clinical EDD — the one your OB-GYN records on your chart — may be adjusted based on ultrasound findings.
If an early ultrasound shows that the embryo size corresponds to a different gestational age than the LMP suggests, your provider may update your EDD to reflect the ultrasound-based dating. This is most commonly done in the first trimester, when ultrasound measurements are most accurate for dating purposes.
After the first trimester, EDD adjustments based on ultrasound become less reliable, because fetal size variation between individuals increases as pregnancy progresses.
What is the difference between EDD and AOG?
EDD is your Estimated Delivery Date — a future date that stays fixed. AOG is your Age of Gestation — a measurement of how far along your pregnancy is right now, expressed in weeks and days from your LMP.
EDD tells you when your baby is expected. AOG tells you where you are in the pregnancy timeline today. Both are calculated from the same LMP date and are used together on your Philippine prenatal record card.
Related calculators
Your EDD connects directly to every other aspect of your pregnancy timeline. These calculators complete the picture:
LMP Calculator — Calculate your EDD, AOG, pregnancy week, and trimester all from your LMP date in one place.
Pregnancy Calculator — Get your full pregnancy timeline including trimester breakdown and week-by-week progress from your LMP.
Ovulation Calculator — Understand when you ovulated, which helps confirm the conception date your EDD is based on.
Period Calculator — Track your cycle to maintain an accurate record of your LMP for future calculations.
BMI Calculator Philippines — Your pre-pregnancy BMI affects recommended weight gain during pregnancy and may influence your delivery plan.
TDEE Calculator — Your daily calorie needs increase during pregnancy. Find your total energy expenditure to support healthy pregnancy nutrition.