Each woman has her own individual timing for ovulation, and it depends on the period needed for the follicle to mature after menstruation. It is considered to be the first phase of the cycle (starting from the 1st day of menstruation to ovulation).
Normally, First phase can be 7-30 days. The second phase (from ovulation to the beginning of the next menstrual period) is constant and usually lasts 14 days. The approximate ovulation date can be calculated by subtracting 14 days from the average menstrual cycle length (MCL). For example, if MCL is 32 days, then the egg release date:
32-14 = 18th day of the cycle.
Formula for calculating the ovulation date in the average menstrual cycle
In order to calculate the ovulation date, you need to know the duration of your average menstrual cycle. This is a calendar method for determining ovulation.
The fact is, that the duration of the second cycle phase (luteal, corpus luteum phase), which begins after the egg release, is constant in every cycle.
Thus, subtracting 14 days (duration of the second phase) from the first day of expected menstruation (on a calendar), would show the approximate ovulation date.
FM – the first day of the last menstruation,
NM – the first day of the next menstruation,
MCL – menstrual cycle length,
O – date of ovulation.
O = (FM + MCL) – 14, where 14 is the average luteal phase duration.
Example: if the first day of the last menstruation was on the 01.05, and the average menstrual cycle length is 30 days
(01.05+30)-14=31.05-14=17.05
Ovulation is expected to occur on the 17th of May.
An important nuance for most accurate ovulation calculation, based on the menstrual calendar!
In order to most accurately calculate the ovulation date – the duration of your second phase has to be known precisely.
14 days – is the average and most common duration of the corpus luteum phase. But, it can vary from 12 to 16 days, which are also normal second phase lengths.
Each woman has her own constant second phase length. But, if the duration of the luteal phase is longer than 16 days or shorter than 12 – medical advice is required.
I recommend(!): Before using the calendar method, that is, the beginning of ovulation after menstruation – it is better to establish the duration of the second phase, based on more accurate calculation methods. Then, the established number should be used in the formula described above – this way, the most probable ovulation period could be calculated precisely.
Is it possible for ovulation to occur a week after menstruation onset?
Ovulation a week after menstruation is absolutely normal, provided that the duration of the corpus luteum phase is 12 or more days. Normally, the menstrual cycle length should be at least 21 days.
Thus, the egg manages to develop by the 7th-9th day of the cycle (21-12=9). So, if menstruation is 2 days long, then by the ninth day the dominant follicle can grow up to 18-22 mm and prepare an egg for ovulation.
If you want to learn more about ovulation immediately after menstruation (7-9th day of the cycle) and the percentage of pregnancies – read this detailed article.
How to calculate ovulation date, if menstrual cycle is irregular?
With an irregular cycle, the calendar method would be informative only when deviation is small – no more than 2-3 days. Thus, when calculating the approximate egg release date, the maximum and minimum values should both be used in the formula.
For example, if the monthly cycle ranges from 28-30 days, then:
(01.05+28)–14=29.05-14=15.05
(01.05+30)–14=31.05-14=17.05
Ovulation is expected to occur between 15th-17th of May.
The chances of conception are high a day or two before ovulation or on the day of ovulation, so it is best to plan accordingly.
In order to calculate accurately the ovulation date when the cycle is irregular – use the several proven methods that I described on this page.
When is the best time for conception?
Sexual intercourse 1-2 days before ovulation or on the day of ovulation assures the maximum chance of conceiving a baby. Next, repeat every 2-3 days. If ovulation, according to the menstruation calendar, would occur on May 17th or May 15th-17th, then the best time for sexual intercourse is as follows: 
To determine the ovulation date after menstruation, if the day of the next menstruation onset is unknown, other methods of determining fertility should be used:
- tests for LH levels;
- salivary ferning test;
- BBT charting;
- folliculometry.
Note(!): There should not be daily sexual intercourse during pregnancy planning. The fact is that spermatozoa mature within 2-3 days and daily ejaculation prevents the majority of male germ cells from developing.
For great detail about menstruation during ovulation and ovulation a few days before the expected menstruation, read this material.
Accurate calculations and successful pregnancy planning!