The easiest way to calculate this, is to follow the schedule above.
If you have an irregular cycle, an ovulation test may provide clarity. These tests measure the LH-spike (LH stands for Luteinizing Hormone) in your urine. Ovulation occurs under the influence of a large amount of LH, in the middle of the cycle. So if there is a lot of this hormone in your urine, you will know that your ovulation is coming. This means that your cycle can last 30 days or longer. The tests are not suitable for everyone. For example, if you have PCOS (a hormonal disorder), the result will often be unjustly positive, because PCOS results in a constantly high level of LH. For women over forty and women with an early menopause, the test result may also be positive without there being a question of ovulation.
Do you not like tests or diagrams? Fortunately, your body will often show certain signs when you are fertile.
The day after your ovulation, your body temperature will rise. If you measure your temperature every morning (around the same time), you will notice that your body temperature is fairly consistent. The day after your ovulation, your body temperature will be higher compared to the measurements before your ovulation (at least 0.2 °C, and this will last for at least 3 days). So if you watch your temperature closely every day, you will be able to tell when your ovulation has occurred.
Your discharge is also a helpful indication of your fertile period. The consistency and clarity of your cervical mucus = (discharge) will change as your ovulation approaches. The usual white discharge will become clear, shiny, more slimy, stringy, and thin. This is good for the sperm cells, which will be able to reach the uterus more easily. This change will start 3 to 4 days before the ovulation, and afterwards your discharge will go back to normal. It may take some getting used to, but if you can use the mucus to make a string of about 10 centimetres between your fingers, you will know that you are fertile.