Hi I m 31 year old. On 12 th day egg size is 18mm n ET is 9.4mm n rigjt ovary has cyst. Then how much chance to get pregant and when should I hv interco?

Correct timing. Natural cycle (no meds?) Start trying today and every other day for the next 4-5 days. This should eb good timing. Impossible to say what your "chance" is without knowing more about you, but chances may be as high as 20%. Good wishes.