Hi, and thanks for your medical question on eHealth forum!
Sperm ejaculated inside the vagina can live for 3-5 days to fertilize the egg. Whereas the ovum only lives for about 24 hours in the fallopian tubes and is available for fertilization. Hence even if you ovulated the next day you can be pregnant. However it is not necessary that all the times this will cause pregnancy. Chances are high. Take a pregnancy test if you miss your periods. Doing a test before that day will usually give negative result.
The earliest you can detect pregnancy is 7th-12th day after conception or ovulation. So if you can time your ovulation then you will have a rough idea as to when to test. Otherwise some women have an implantation bleeding usually in the later part of third week or early part of 4th week since the last menstrual period. It usually occurs any time between 7th-12th day after conception. Hence a very sensitive urine test or a blood pregnancy test can detect this 4-5 days before the next due date. Take care!