How long aftet sex can you test if your not positive when to expect your period?

? test for pregnancy. Most of the consumer kits can show positive as close to a day or two after conception - so i would wait at least 2 days after unprotected intercourse to check. If you don't want to be pregnant - you need to use some sort of protection.
I'm assuming... Your question was worded such that i think you want to know how soon you can test after missing a period secondary vto becoming pregnant. Most commercial kits are positive within one to two weeks after a missed period. Laboratory tests are sooner, but expensive. Missed periods are quite common.
Every test different. Over the counter tests give you the time. Serum tests by a lab can be done at anytime.