I had protected intercourse during unsafe days 6th january and my period date is 18th of every month and ejaculation was outside so i don't know whether condom had leakage or not. in this case pregnancy is possible from precum or not?

Precum does not have sperms. No sperms (ejaculation) inside vagina no pregnancy. Cant comment on whether the condom had a leak or not

Condoms are highly effective to prevent pregnancy. If the condom was used correctly then pregnancy is very unlikely.

Conception occurs within day or so of the sex. It takes about 3 weeks for the embryo to make enough HCG for a positive pregnancy test. Blood test may be done a day after a missed period. Home pregnancy tests should be done 4-5 days after the missed period. If the result is negative repeat the test in 4-5 days. Use first morning urine and follow instructions for the test carefully.