Thank you for your query at AskTheDoctor.com
I understand your concern.
Pregnancy or fertilization occurs at the time of ovulation. So any unprotected intercourse prior to ovulation can lead to pregnancy. The ovum once released stays viable for 12 hours, and any contact with semen can lead to fertilization and subsequent pregnancy.
Since you were one day before the last day of your cycle, and considering your cycles are regular ( 28-35 days every period cycle ), ovulation occurred long back and there are no chances of pregnancy.
Also if you get your period on time you should not worry about pregnancy at all.
Always try to avoid unprotected intercourse between the 8th-22nd day of your cycle, so that even if ovulation occurs a little later or before, you can avoid getting pregnant.
Hope this was helpful,
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