An online pregnancy calculator will help you determine your gestational age and estimated due date based on the date of your last menstrual period, conception or IVF
An online pregnancy calculator will help you determine your gestational age and estimated due date based on the date of your last menstrual period, conception or IVF
The calculation is based on a standard pregnancy length of 40 weeks (280 days) from the first day of the last menstrual period.
The pregnancy calculator is a convenient tool for determining your pregnancy duration and expected due date. It will help you track the progress of your pregnancy and plan important events.
The calculator supports three calculation methods: by the date of the last menstruation (the most common), by the date of conception (more accurate if the date is known) and by the date of IVF (for cases of in vitro fertilization). Each method has its own accuracy and calculation features.
Let's look at practical examples of calculating gestational age and expected date of birth for different methods:
Last menstruation began on January 1, 2024
Входные данные:
PM date: January 1, 2024Расчёт:
Deadline = PM + 280 days = January 1, 2024 + 280 daysEstimated due date: October 7, 2024
Today (April 1, 2024): 13 weeks pregnant
First trimester (0-12 weeks)
Days until delivery: 190 days
The exact date of conception is known - January 15, 2024
Входные данные:
Date of conception: January 15, 2024Расчёт:
Duration = Date of conception + 266 days = January 15, 2024 + 266 daysEstimated due date: October 7, 2024
Today (April 1, 2024): 11 weeks pregnant
First trimester (0-12 weeks)
Days until delivery: 189 days
The embryo transfer took place on February 10, 2024
Входные данные:
Transfer date: February 10, 2024Расчёт:
Due date = Transfer date + 14 days (pregnancy age) + 266 days = February 10 + 280 daysEstimated due date: November 17, 2024
Today (April 1, 2024): 7 weeks pregnant
First trimester (0-12 weeks)
Days until delivery: 230 days
PM was November 15, 2023, today is April 1, 2024
Входные данные:
PM date: November 15, 2023Расчёт:
Deadline = November 15, 2023 + 280 days = August 22, 2024Estimated due date: August 22, 2024
Today (April 1, 2024): 20 weeks pregnant
Second trimester (13-26 weeks)
Days until delivery: 144 days
PM was June 10, 2024, today is March 15, 2025
Входные данные:
PM date: June 10, 2024Расчёт:
Deadline = June 10, 2024 + 280 days = March 17, 2025Estimated due date: March 17, 2025
Today (March 15, 2025): 39 weeks pregnant
Third trimester (27-40 weeks)
Days until delivery: 2 days
PM was September 1, 2024, twins, today is January 1, 2025
Входные данные:
PM date: September 1, 2024 (multiple pregnancy)Расчёт:
Deadline = September 1, 2024 + 266 days (usually shorter for twins) = May 24, 2025Estimated due date: May 24, 2025 (dues are usually earlier for twins)
Today (January 1, 2025): 17 weeks pregnant
Second trimester (13-26 weeks)
Days until delivery: 144 days (multiple pregnancies often end at 37-38 weeks)
There are several ways to determine the gestational age, each of which has its own characteristics and accuracy.
Pregnancy is divided into three trimesters, each of which has its own characteristics of fetal development and changes in the mother’s body.
It is important to understand that the due date is approximate. Only 5% of women give birth exactly on the expected date.
During pregnancy, it is important to monitor your health by eating right, engaging in moderate physical activity, and visiting your doctor regularly.
Our free pregnancy calculator will help you determine your gestational age and estimated due date. Simply choose a calculation method, enter the date and get detailed information about your pregnancy.
The gestational age based on the date of the last menstruation (LMP) is calculated from the first day of the last menstruation. 280 days (40 weeks) are added to this date to give the estimated due date. For example, if PM began on January 1, then the expected date of birth is October 7 of the same year. This method is the most common, but has an accuracy of ±7 days.
The estimated due date (EDD) is a rough estimate. Only 5% of women give birth exactly in the PDR. Childbirth is considered normal between 37 and 42 weeks of pregnancy (full-term pregnancy). Most women give birth between 38 and 41 weeks. The accuracy depends on the calculation method: PM (±7 days), date of conception (±5 days), IVF (±3 days).
When calculating the gestational age from the date of conception, 266 days (38 weeks) are added to the date of conception, since conception usually occurs approximately 2 weeks after the start of the last menstrual period. This method is more accurate (±5 days) if the exact date of conception is known. For example, if conceived on January 15, the expected due date is October 7.
With IVF (in vitro fertilization), the gestational age is calculated from the date of embryo transfer. To this date, 14 days are added (to take into account the age of the embryo during transfer) and 266 days of standard pregnancy, for a total of 280 days. This is the most accurate method (±3 days), since the transfer date is known exactly. For example, if the PDR is postponed on February 10, it will be approximately November 17.
A trimester is a period of pregnancy lasting about 13 weeks. First trimester: 0-12 weeks (organ formation), second trimester: 13-26 weeks (active growth), third trimester: 27-40 weeks (preparation for childbirth). The trimester is determined by the current stage of pregnancy. For example, at week 20 - the second trimester, at week 32 - the third trimester.
A normal pregnancy lasts from 37 to 42 weeks (259-294 days) from the first day of the last menstrual period. The average duration is 40 weeks (280 days). Pregnancy after 37 weeks is considered full-term. Childbirth before 37 weeks is premature, after 42 weeks - post-term. Only 5% of women give birth exactly on the expected date (40 weeks).
The gestational age in weeks is calculated from the first day of the last menstrual period to the current date. For example, if PM was January 1st, and today is April 1st, then approximately 13 weeks have passed. The calculator automatically determines your gestational age when you enter the date. You can also calculate: (current date − PM date) / 7 days = number of weeks.
The obstetric period is counted from the first day of the last menstruation (40 weeks = 280 days). Embryonic period - from the moment of conception (38 weeks = 266 days). The difference is about 2 weeks, since conception occurs approximately 2 weeks after the start of the menstrual cycle. Doctors use the obstetric date, so it is the standard for calculating the due date.
Determining the exact date of conception is difficult, since fertilization can occur within several days after ovulation, and sperm live in a woman’s body for up to 5 days. However, if the date of ovulation is known (by tests, ultrasound or measurement of basal temperature), then conception usually occurs on the day of ovulation or within 1-2 days after it.
For twins (multiple pregnancies), the calculation of the due date is similar, but birth usually occurs earlier - at 37-38 weeks of pregnancy. The expected date of birth is calculated as usual (from PM + 280 days), but often birth occurs 2-3 weeks earlier. This is due to the fact that the uterus stretches more when carrying several fetuses.
The accuracy of calculating the date of birth depends on several factors: the calculation method (IVF ± 3 days, conception ± 5 days, PM ± 7 days), the regularity of the menstrual cycle, the accuracy of knowing the date of the last menstruation or conception, and the individual characteristics of the woman’s body. Also influenced by: first or repeat pregnancy, mother’s age, health status, genetic factors.
Doctors use the date of the last menstrual period (LMP) because it is more accurately known to most women than the date of conception. This is a standard method accepted in obstetrics throughout the world. The method is based on the fact that the menstrual cycle begins on the first day of menstruation, and ovulation occurs approximately 2 weeks later. This allows us to unify calculations for all women.
The number of days until delivery is calculated as the difference between the expected date of birth and the current date. For example, if the birth date is October 7, and today is April 1, then the time left until the birth is: October 7 - April 1 = approximately 190 days. The calculator automatically calculates this value when you enter the current date. A negative value means that the pregnancy is post-term.
Yes, the estimated date of birth can be adjusted by the doctor after the first ultrasound at 11-13 weeks, when the size of the fetus and its gestational age are accurately determined. An ultrasound may show that the actual gestational age differs from the PM calculation by several days. In this case, the doctor can recalculate the maximum allowance. Typically the correction is ±5-7 days.
The online pregnancy calculator works according to standard formulas: to calculate, it adds 280 days from the PM, 266 days from the date of conception, 280 days from the date of IVF, taking into account the age of the embryo. The calculator determines the current gestational age, trimester, number of days until delivery and expected due date. All calculations are based on standard obstetric techniques.
The most accurate calculation method is based on the date of IVF (in vitro fertilization), accuracy ±3 days, since the date of embryo transfer is known exactly. The second most accurate is by the date of conception (±5 days), if it is known exactly. Less accurate - by the date of the last menstruation (±7 days), but it is the most common, since most women know this date.
Pregnancy lasts approximately 9 months (with a standard 30 days per month). First month: 0-4 weeks, second: 5-8 weeks, third: 9-13 weeks, fourth: 14-17 weeks, fifth: 18-22 weeks, sixth: 23-27 weeks, seventh: 28-31 weeks, eighth: 32-36 weeks, ninth: 37-40 weeks. However, a month is an approximate unit; it is more accurate to count by weeks.
A pregnancy calendar is a tool for tracking the progress of your pregnancy by week and month. It shows what changes occur in the fetus and the mother’s body at each stage, what examinations need to be carried out, which symptoms are normal, and which require seeing a doctor. The pregnancy calculator automatically detects the current week and shows relevant trimester information.
With an irregular cycle, calculation based on the date of the last menstruation is less accurate. In this case, it is better to use the date of conception (if known), an ultrasound in the first trimester (11-13 weeks) to determine the exact date, or the date of IVF (the most accurate method). The first ultrasound gives the most accurate gestational age, regardless of the regularity of the cycle. The doctor can correct the PDR after an ultrasound.
Calculating the gestational age after a cesarean section is no different from usual. The same method is used - from the first day of the last menstruation or from the date of conception. A previous caesarean section does not affect the length of the next pregnancy. However, it is important to consider that after a cesarean, the next cesarean may be planned at 38-39 weeks, but this is decided by the doctor.
To find out the current week of pregnancy, enter the date of your last menstrual period into the calculator or calculate manually: (today's date - PM date) / 7 days. For example, if PM was January 1, and today is February 22, then: (February 22 − January 1) / 7 = approximately 7-8 weeks of pregnancy. The calculator automatically shows the current week and day of pregnancy.
Pregnancy weeks are counted from the first day of the last menstrual period. The first week is the first week of the menstrual cycle (menstrual period). The second week is the follicular phase of the cycle (preparation for ovulation). Ovulation occurs at the end of the second or beginning of the third week. Conception usually occurs at 2-3 weeks, but the countdown of pregnancy begins from the first week (from the first day of PM).
During pregnancy, after stimulation of ovulation, the calculation is similar to the usual one - from the first day of the last menstruation + 280 days. If the exact date of ovulation is known (according to ultrasound monitoring), you can use it for a more accurate calculation: ovulation date + 266 days. However, the standard PM method remains the main one. It is important to inform your doctor about stimulation for correct management of pregnancy.
The due date is called the estimated due date (ETD) because it is an estimate rather than the exact moment of delivery. Only 5% of women give birth exactly in the PDR. The normal delivery range is from 37 to 42 weeks of pregnancy (3 weeks before and 2 weeks after PPD). The exact date of birth cannot be predicted due to individual characteristics of the body, health factors of the mother and fetus, and genetics.
Doctors use weekly calculations because they are more accurate. Pregnancy is divided into 40 weeks (280 days). Calculation by month is inaccurate, since months have different numbers of days (28-31 days). However, for ease of understanding, they use: 1st trimester ≈ 3 months, 2nd trimester ≈ 3 months, 3rd trimester ≈ 3 months. The exact period is always indicated in weeks: for example, 20 weeks 3 days.
If the date of your last menstrual period is unknown, use other methods: date of conception (if known) + 266 days, date of first positive pregnancy test (approximately 4 weeks of pregnancy), first ultrasound at 11-13 weeks (the most accurate method for determining due date), date of IVF, if used. The first ultrasound gives the most accurate gestational age and can be used by a doctor to determine the PDR.
The normal pregnancy period is from 37 to 42 weeks (259-294 days from the first day of PM). Accordingly, the normal number of days until delivery decreases as pregnancy progresses. For example, at 30 weeks before birth there are approximately 70 days, at 37 weeks - 21 days (beginning of full-term pregnancy), at 40 weeks - about 0 days (PDF). Childbirth after 42 weeks is considered post-term.
To calculate the PDA manually, use Naegele's rule: subtract 3 months from the first day of the last menstruation and add 7 days. For example, PM was January 1: January 1 − 3 months = October 1 (previous year), + 7 days = October 8. Or simply: PM date + 280 days = PDR. This method gives an approximate date with an accuracy of ±7-14 days.
The gestational age of the fetus is the gestational age calculated from the first day of the last menstrual period. It is measured in weeks and days: for example, 20 weeks 3 days. Gestational age is used to determine whether fetal development is normal, plan examinations, and establish the expected date of birth. Differs from embryonic age by about 2 weeks (embryonic age - from conception).
When pregnant with a donor egg, the calculation is similar to IVF: from the date of embryo transfer + 280 days (taking into account the age of the embryo at the time of transfer). If the date of the donor's last menstrual period is known, the standard method can be used, but the calculation from the date of transfer will be more accurate. The doctor performing IVF must provide an exact date for calculating the PDR.
0-12 нед
Первый триместр
13-26 нед
Второй триместр
27-40 нед
Третий триместр