My partner and i had sex and the condom broke without us realising and he cum inside me. i was on day 20 of my 28 day cycle. i didnt take a plan b i know it doesnt work after ovulation. what are the chances im pregnant?

Pregnancy is know to have occurred from sex on any and all days of the menstrual cycle. If sex took place less than 72 hours ago, take Plan B. If you miss your period by 4-5 days, do a home pregnancy test. If the result is negative repeat the test 4-5 days later unless you get a period by then. Use first morning urine and follow the instructions carefully. Wish you good health! Use contraceptive.

If you have regular 28-30 day cycle every month, chance of conception is relatively low but it cannot be ruled out.