Hi Hun, HPTs are usually effective from about the first day that your period is late… but that’s just “usually”… sometimes they’re so unreliable that they don’t pick up anything. So the most effective test would be a blood test that you can get from your GP.
ALso, remember that stress, weight loss, change in diet, medication and a whole lot of other things can cause your period to be late or can immitate pregnancy symptoms.
So, to be 100% sure, get a blood test done.
Hope this helped
Eva