This AOG calculator tells you your Age of Gestation — the exact number of weeks and days your pregnancy has progressed since your last menstrual period.
AOG is the number written on your prenatal record card at every check-up in the Philippines. It tells your OB-GYN exactly where you are in your pregnancy at any given visit, guides clinical decisions, and determines whether your baby’s development is on track. Enter your LMP date below and get your current AOG instantly.
What your AOG means:
Your AOG is expressed in weeks and days — for example, 12+3 means 12 weeks and 3 days of gestation from your LMP. This is exactly how it appears on your Philippine maternity record card.
AOG increases by one day every day. It does not change based on your due date or any other factor. It simply measures how many days have passed since the first day of your last menstrual period, converted into weeks and days.
What is AOG in pregnancy — and why is it on your prenatal card?
AOG stands for Age of Gestation. It is the clinical measurement of how far along a pregnancy is, counted from the first day of the last menstrual period (LMP) and expressed in completed weeks plus remaining days.
If you have attended a prenatal check-up at a Philippine hospital, clinic, or barangay health center, you have seen AOG written on your record card — usually as a number like 8+3 or 20+0. The number before the plus sign is the completed weeks of pregnancy. The number after is the additional days beyond those completed weeks.
AOG is one of the most fundamentally useful numbers in obstetric care because it provides a single, consistent reference point for everything that happens during pregnancy. When your OB-GYN says your baby's measurements are appropriate for AOG, they mean the fetal size matches what is expected at your current stage. When a scan report says measurements are small for AOG or large for AOG, it means the measurements differ from what is expected at your gestational age.
AOG is also the basis for scheduling your prenatal visits, timing your anatomy scan, planning your delivery, and identifying when a delivery would be considered preterm or full term. Every clinical decision in prenatal care is referenced against AOG.
AOG calculation formula — how to calculate AOG from LMP
The AOG calculation formula is one of the simplest in obstetrics, which is part of why it is so widely and consistently used.
Step 1: Count the total number of days from the first day of your last menstrual period to today's date.
Step 2: Divide that total by 7.
Step 3: The whole number result is your completed weeks of gestation. The remainder is your additional days.
AOG = (Today's date minus LMP date) divided by 7, expressed as weeks and days.
This is the complete AOG calculation formula. There are no multipliers, no adjustments, and no additional variables — just the number of days since your LMP, converted into weeks and days.
Example: LMP of January 1. Today is March 1. That is 59 days. 59 divided by 7 gives 8 weeks with a remainder of 3 days. AOG = 8 weeks and 3 days, written as 8+3.
Our AOG calculator does this automatically from your LMP date — no manual counting required.
How to calculate AOG manually — step by step
Knowing how to calculate AOG manually is useful when you want to verify a result, understand what your record card says, or simply know your AOG without access to a calculator.
Method 1 — Count days and divide
This is the most accurate manual method:
Take the first day of your last menstrual period. Count every day from that date to today, including both the start date and today. Divide the total by 7. The quotient is your completed weeks. The remainder is your additional days.
Example using LMP of October 15 and today being March 1:
October has 31 days. From October 15 to October 31 = 16 days. November = 30 days. December = 31 days. January = 31 days. February = 28 days. March 1 = 1 day. Total = 16 + 30 + 31 + 31 + 28 + 1 = 137 days.
137 divided by 7 = 19 weeks with a remainder of 4 days. AOG = 19+4.
Method 2 — Use a calendar and count weeks directly
A quicker but slightly less precise method is to count the weeks directly on a calendar from your LMP date.
Find your LMP date on a calendar. Count forward one week at a time, marking each completed week. When you reach today's date, count the remaining days in the current incomplete week.
This method is easier to do mentally but can be off by a day if you are not careful about which day the week starts and ends. For clinical purposes, the day-counting method above is more reliable.
How AOG is written on your prenatal record
AOG is always written in weeks+days notation in Philippine prenatal records. The convention is:
Completed weeks, a plus sign, then remaining days. So 19 weeks and 4 days is written as 19+4. Eight weeks and zero days is written as 8+0. Thirty-two weeks and one day is written as 32+1.
When your OB-GYN asks your AOG at a check-up, they are asking for this number. Having it ready — either calculated from this tool or looked up on your record card — makes your prenatal visit run more smoothly.
AOG and its relationship to EDD and gestational age
AOG, gestational age, and pregnancy weeks are all different names for the same measurement. In the Philippines, the term AOG is most commonly used in clinical settings. Internationally, gestational age is the more widely used term. Pregnancy week is the term most commonly understood by patients and used in popular pregnancy tracking.
All three measure the same thing: the number of weeks and days that have passed since the first day of the last menstrual period.
AOG is related to your EDD (Estimated Delivery Date) in a simple way. Your EDD corresponds to 40+0 — 40 weeks and 0 days of gestation. When your AOG reaches 40+0, you are at your due date.
You can work backward from your EDD to find your AOG on any given date. If today is 10 weeks before your EDD, your AOG is 30+0. If today is 5 weeks and 3 days before your EDD, your AOG is 34+4.
Our AOG calculator shows you both your current AOG and your EDD alongside each other, so you always have the complete picture at a glance.
What AOG numbers mean for your pregnancy
AOG 1+0 to 12+6 — First trimester
The first trimester runs from AOG 1+0 through 12+6. This is the period of most critical development, when the embryo forms all its major organs, structures, and systems.
Early pregnancy symptoms are typically most intense during the first trimester — nausea, fatigue, breast tenderness, and food aversions are all common. The first prenatal visit, early blood tests, and the first ultrasound all typically fall within this AOG range.
The risk of miscarriage is highest in the first trimester and drops significantly after week 12. By the end of the first trimester, most major structural development is complete.
AOG 13+0 to 26+6 — Second trimester
The second trimester runs from AOG 13+0 through 26+6. This is generally the most comfortable phase of pregnancy for most women.
The anatomy scan — the detailed ultrasound that checks fetal development — is typically scheduled between AOG 18+0 and 20+0. Fetal movement is first felt by most mothers between AOG 18+0 and 22+0.
By AOG 24+0, a baby has reached the threshold of viability — the point at which, with intensive medical care, survival outside the womb becomes possible, though premature delivery at this stage carries significant risks.
AOG 27+0 to 36+6 — Third trimester (early to mid)
From AOG 27+0, the pregnancy enters the third and final trimester. The focus shifts from organ development to growth — the baby gains most of its birth weight during this period.
Prenatal visits become more frequent in the third trimester, increasing from monthly to every two weeks from AOG 28+0, then weekly from AOG 36+0.
The baby's position in the uterus becomes increasingly relevant as the AOG approaches term, and your OB-GYN will assess whether the baby is in the optimal head-down position for delivery.
AOG 37+0 to 42+0 — Full term
A baby born at AOG 37+0 or later is considered full term. AOG 37+0 to 38+6 is early term. AOG 39+0 to 40+6 is full term. AOG 41+0 to 41+6 is late term. AOG 42+0 and beyond is post-term.
Most OB-GYNs in the Philippines will recommend closer monitoring — and potentially induction of labour — when AOG reaches 41+0, particularly if there are any clinical concerns about maternal or fetal wellbeing.
Calculating AOG in Philippine prenatal care — practical context
AOG is a central part of every prenatal record in the Philippines. Whether you are attending a private OB-GYN, a government hospital, a lying-in clinic, or a barangay health center, your AOG will be calculated, recorded, and referenced at every visit.
Your maternity record card has a column for AOG at each visit date. Your OB-GYN uses the AOG on each visit date to assess whether your fundal height — the measurement from the pubic bone to the top of the uterus — is appropriate. Fundal height in centimeters typically matches the AOG in weeks after about 20 weeks, so a fundal height of 28 cm at AOG 28+0 is considered normal.
AOG is also used to interpret ultrasound measurements. When an ultrasound report compares fetal biometry measurements to gestational age norms, it is comparing your baby's actual measurements to the expected measurements for your AOG. Being within two weeks of the AOG-based expectation is generally considered normal variation.
If you are delivering at a PhilHealth-accredited facility, your AOG at delivery is recorded on your delivery record and affects clinical classifications used for PhilHealth reimbursement and statistical reporting.
How do you calculate AOG without knowing your exact LMP?
Not knowing your exact LMP date is more common than many women realise — particularly if cycles were irregular, if the last period was unusually light or short, or if pregnancy was not planned and the LMP was not noted at the time.
There are several ways to estimate your AOG when the LMP date is uncertain.
Use an early ultrasound measurement. A first-trimester ultrasound, particularly between 7 and 12 weeks, measures the crown-rump length of the embryo. This measurement is highly accurate for dating the pregnancy and can give you an AOG estimate within approximately five days. Your OB-GYN can calculate an estimated LMP equivalent from this measurement, which you can then use in this calculator.
Estimate from a positive pregnancy test. If you know when you first got a positive pregnancy test, you can estimate that you were approximately 4 to 5 weeks AOG at that time, since hCG levels sufficient to trigger a test typically accumulate around 4 weeks from the LMP. Subtract 4 to 5 weeks from your test date to estimate your LMP.
Use cycle tracking data. If you were tracking your cycle before pregnancy — through period tracking, temperature charting, or ovulation testing — your last recorded ovulation or period date can serve as the starting point for AOG calculation.
Frequently asked questions
How do I calculate AOG?
Count the number of days from the first day of your last menstrual period to today. Divide that number by 7. The whole number is your completed weeks of gestation. The remainder is your additional days. Write it as weeks+days — for example, 16+2 for 16 weeks and 2 days.
Our AOG calculator does this automatically from your LMP date. Enter your LMP below and your AOG appears instantly in the same format used on your Philippine prenatal record card.
What does AOG 8+3 mean?
AOG 8+3 means 8 weeks and 3 days of gestation from your last menstrual period. You are in your ninth week of pregnancy. The 8 represents completed weeks, and the 3 represents the additional days into the current incomplete week.
This notation — weeks plus days — is standard in Philippine obstetric records. Every whole number before the plus represents a completed week. The maximum days after the plus is always 6, because 7 days completes a new week.
How is AOG different from EDD?
AOG is a measure of where you are in your pregnancy right now — it increases every day. EDD is a fixed future date — it stays the same throughout your pregnancy.
AOG 40+0 corresponds to the EDD. When your AOG reaches 40 weeks and 0 days, you are at your estimated due date. Before that, your AOG tells you how far along you are. After that, your AOG tells you how post-term you are.
Can AOG be calculated without LMP?
Yes — an early first-trimester ultrasound can provide a gestational age estimate that serves the same function as an LMP-based AOG calculation. Ultrasound-derived gestational age is measured from the crown-rump length of the embryo and is accurate to within about 5 days in the first trimester.
Your OB-GYN will typically establish an AOG from the ultrasound if your LMP date is unknown or if the ultrasound measurement suggests your AOG differs significantly from what the LMP date implies.
What is a normal AOG for delivery?
A full-term delivery occurs between AOG 37+0 and 42+0. Delivery before AOG 37+0 is preterm. Delivery after AOG 42+0 is post-term.
Within the full-term range, AOG 39+0 to 40+6 is considered the optimal delivery window for the best outcomes for most babies. However, every pregnancy is individual, and the appropriate AOG for delivery depends on the specific clinical situation assessed by your OB-GYN.
Why is AOG important in Philippine prenatal care?
AOG is the foundation of all prenatal care decisions in the Philippines. It determines the schedule of prenatal visits, the timing of recommended tests and scans, the interpretation of fetal growth measurements, and the management of any complications that arise.
AOG is also used to classify deliveries for PhilHealth coverage purposes and is recorded on all government health statistics related to maternal and infant care. It is one of the most universally referenced numbers in Philippine obstetric practice.
Related calculators
Your AOG connects directly to every other aspect of your pregnancy care. These calculators complete the picture:
LMP Calculator — Calculate your AOG, EDD, pregnancy week, and trimester all from your LMP date in one place.
EDD Calculator — Find your Estimated Delivery Date from your LMP or conception date, using the same LMP that gives you your AOG.
Pregnancy Calculator — Get your full pregnancy timeline including week-by-week progress and trimester breakdown.
Ovulation Calculator — Understand your fertile window — the period when the pregnancy that determined your AOG began.
Period Calculator — Track your menstrual cycle to maintain an accurate LMP date for AOG calculations in future pregnancies.
BMI Calculator Philippines — Your pre-pregnancy BMI is recorded alongside your AOG at your first prenatal visit and guides recommended weight gain during pregnancy.
TDEE Calculator — Your daily calorie needs increase at different stages of pregnancy. Your AOG helps you understand which stage you are at and what your nutritional needs are now.