This pregnancy calculator tells you your estimated due date, how many weeks pregnant you are right now, and which trimester you are in — all from one simple input.
Whether you are just finding out you are pregnant or tracking your progress week by week, knowing your due date and pregnancy timeline is one of the first things every expectant mother needs. Enter the first day of your last menstrual period below and get your complete pregnancy timeline instantly.
What your results mean:
Your estimated due date is calculated using Naegele’s Rule — the same method used by OB-GYNs and midwives in the Philippines and worldwide. It is an estimate, not a fixed date. Most babies are born within two weeks before or after this date, and only around 5% of babies arrive exactly on their due date.
Your pregnancy week tells you how far along you are today. Pregnancy is counted from the first day of your last menstrual period, not from conception — which is why you may feel a week or two behind when you first find out.
What is a pregnancy calculator — and how does it work?
A pregnancy calculator is a tool that uses the date of your last menstrual period (LMP) to estimate three things: your due date, how many weeks and days pregnant you are today, and which trimester of pregnancy you are currently in.
It works using a formula called Naegele’s Rule, which has been used in obstetric practice for over 200 years. The formula is straightforward: add 280 days (40 weeks) to the first day of your last menstrual period. The result is your estimated delivery date, also called your EDD.
The reason pregnancy is counted from your LMP rather than from conception is practical — most women know the date of their last period far more reliably than the date of conception. Ovulation and conception typically happen around 14 days after the start of your LMP, which is already built into the 40-week calculation.
How to calculate your pregnancy due date
Using your last menstrual period (LMP)
This is the most common and reliable method for calculating your due date when you are in the early weeks of pregnancy.
Enter the first day of your last menstrual period into the calculator above. The calculator adds 280 days to that date and gives you your estimated due date.
Example: If your last menstrual period started on January 1, your estimated due date would be October 8.
What if I do not know my LMP?
If you are unsure of your last menstrual period date, your OB-GYN or midwife can estimate your due date using an ultrasound. An early ultrasound — typically done in the first trimester — measures the size of the embryo and estimates gestational age from there.
An ultrasound due date is often considered more accurate than LMP-based calculation, particularly for women with irregular menstrual cycles, because LMP-based calculation assumes a standard 28-day cycle with ovulation on day 14.
What if my cycle is longer or shorter than 28 days?
Naegele’s Rule assumes a 28-day menstrual cycle. If your cycle is regularly longer or shorter than 28 days, your actual ovulation date — and therefore your conception date — may be different from the standard assumption.
For cycles that differ significantly from 28 days, an early ultrasound gives a more accurate due date than LMP calculation alone. Discuss this with your doctor at your first prenatal visit.
Understanding your pregnancy timeline
Trimesters of pregnancy
Pregnancy is divided into three trimesters, each roughly three months long:
First trimester: Weeks 1 to 12. This is the period of most rapid fetal development. The major organs, heart, brain, and limbs begin to form. This is also when most morning sickness occurs.
Second trimester: Weeks 13 to 26. Often called the most comfortable trimester. Morning sickness typically eases, energy returns, and the baby’s movements become noticeable. Gender can usually be determined by ultrasound during this period.
Third trimester: Weeks 27 to 40. The baby gains most of its weight during this period. Discomfort increases as the baby grows, and the body begins preparing for labour.
Pregnancy weeks explained
Pregnancy is measured in weeks from the first day of your last menstrual period. A full-term pregnancy is 40 weeks — though anywhere from 37 to 42 weeks is considered normal.
When your doctor or midwife asks how many weeks pregnant you are, they are counting from your LMP — not from when you got a positive pregnancy test or when you believe conception occurred. This is why it is common to be told you are 4 or 5 weeks pregnant before you even miss a period.
Our pregnancy calculator shows your exact week and day count so you always know precisely where you are in your pregnancy journey.
Pregnancy due date for Filipino mothers — what to expect
The estimated due date is the same calculation worldwide — 40 weeks from your last menstrual period — but your prenatal care journey in the Philippines has its own timeline and considerations.
In the Philippines, the Department of Health recommends a minimum of 8 prenatal visits during pregnancy. These are typically scheduled at:
First visit: As early as possible in the first trimester — ideally before 12 weeks.
Second and third visits: During the second trimester.
Remaining visits: Monthly in the third trimester, increasing to weekly as your due date approaches.
Your barangay health center, lying-in clinic, or OB-GYN can help you plan your prenatal visits from your first confirmation of pregnancy. Knowing your due date from this calculator gives you a clear timeline to plan around from the very start.
Pregnancy symptoms week by week — what is normal
First trimester symptoms (weeks 1 to 12)
Morning sickness — nausea and sometimes vomiting — is the most commonly reported early pregnancy symptom. Despite the name, it can occur at any time of day. It typically peaks around weeks 8 to 10 and eases by the end of the first trimester for most women.
Other common first trimester symptoms include extreme fatigue, breast tenderness, frequent urination, food aversions or cravings, and light spotting around the time of implantation.
Second trimester symptoms (weeks 13 to 26)
The second trimester is generally the most comfortable period of pregnancy for most women. Energy levels typically improve, morning sickness fades, and the visible baby bump begins to show.
Around weeks 18 to 22, most first-time mothers begin to feel fetal movement — a sensation often described as fluttering or bubbling. Women who have been pregnant before may notice movement slightly earlier.
Third trimester symptoms (weeks 27 to 40)
As the baby grows larger, physical discomfort increases. Back pain, difficulty sleeping, frequent urination, and swollen feet and ankles are common. Braxton Hicks contractions — practice contractions — may begin during this period.
In the final weeks before your due date, your body begins preparing for labour. Signs that labour may be approaching include the baby dropping lower in your pelvis, increased Braxton Hicks contractions, and changes in vaginal discharge.
Frequently asked questions
How do I calculate my pregnancy due date?
The simplest way to calculate your pregnancy due date is to add 280 days to the first day of your last menstrual period. Our pregnancy calculator does this automatically — enter your LMP date and your estimated due date appears instantly.
This calculation is called Naegele’s Rule and is the standard method used by doctors and midwives in the Philippines and worldwide.
How accurate is a pregnancy calculator?
A pregnancy calculator based on your LMP gives you an estimated due date — not a guaranteed date. Around 80% of babies are born within two weeks either side of the calculated due date.
The accuracy depends on how regular your menstrual cycle is. Women with a regular 28-day cycle will get the most accurate estimate. Women with irregular cycles or uncertain LMP dates are better served by an early ultrasound for due date confirmation.
What is the difference between AOG and EDD?
AOG stands for Age of Gestation — the number of weeks and days your pregnancy has progressed from your last menstrual period. It is the same as your pregnancy week count.
EDD stands for Estimated Delivery Date — your due date. These are the two most common terms you will see on your prenatal records in the Philippines, and both are calculated from your LMP.
What is LMP in pregnancy?
LMP stands for Last Menstrual Period. It refers to the first day of your most recent period before you became pregnant. Your LMP is the starting point for calculating your due date, your AOG, and your entire pregnancy timeline.
When your doctor asks for your LMP, they are asking for this specific date — not when your period ended, but when it started.
Can I be pregnant before my missed period?
Yes. By the time most women take a pregnancy test after a missed period, they are already 4 to 5 weeks pregnant by LMP dating — even though conception only occurred about 2 weeks earlier.
Some pregnancy tests are sensitive enough to detect the pregnancy hormone hCG before a missed period. However, the earliest reliable time to test is typically the first day of your expected period.
What week is the due date?
Your due date falls at exactly 40 weeks of pregnancy, counted from the first day of your last menstrual period. Babies born anywhere between 37 weeks and 42 weeks are considered full term. Births before 37 weeks are preterm, and births after 42 weeks are post-term.
Related calculators
Your pregnancy timeline is the starting point. These related calculators help you through each stage:
BMI Calculator Philippines — Check your pre-pregnancy BMI, which your OB-GYN may use to guide recommended weight gain during your pregnancy.
TDEE Calculator — Find your total daily calorie burn. This is the foundation for any weight management plan.
Calorie Deficit Calculator — Build a daily calorie target to move your BMI toward a healthier range at a safe, sustainable pace.
Ideal Weight Calculator — Find the specific weight target that corresponds to a healthy BMI for your height.
Body Fat Percentage Calculator — Get a deeper look at your body composition beyond what BMI alone can show.
BMR Calculator — Understand your minimum daily calorie needs, the foundation beneath any calorie management plan.
Macro Calculator — Split your daily calories into the right amounts of protein, carbs, and fat for your goal.