The first 7 days of your cycle are usually safe as the eggs are not mature yet. Of course, you might be experiencing bleeding in the first 3-4 days and intercourse might not be preferred during this time. The first 3-4 immediate days after periods should be your target then. Similarly, the last few days of your cycle – the days after day 21 – are also considered to be safe days because by then the mature egg, which has a lifespan of one day, would have withered away. Now this period is safe for women who have a cycle length of 28 or lesser days, and they generally ovulate on the mid-term. For women whose cycle length varies, or is greater than 28 days, this safe period is not valid.
If the above calculations are confusing for you, there are many online “safe period” calculators available which will predict your safe period