Stupid question how do cheap tests work?

[incognitony]

My sister found out she was preg last month so she gave me her cheap (strips) preg tests. They expire this month so I started testing for "fun" around 8dop I have over 20 test that expire in a few days. My "fun" testing hasn't been very fun seeing bfn after bfn. My question is today again I had a bfn (11dpo) the sensitivity is 20hcg. Because I'm not even seeing a faint line does it mean I'm prob out for this month? Would a faint line show if I had an hcg of say 10 or 15?? I was going to use a frer tomorrow should i, or will it be a waste of a test?

[starburst604]

It's quite possible to not see a line at 11dpo. I wouldn't waste pricier tests if you have cheapies to use up. I only bought an FRER after I got a positive on a wondfo and wanted to double confirm.

[achi]

Yup, ditto starburst. I used dollar store tests (was out of wondfos) and then bought a clear blue digital after I got a BFP two days in a row.

[tiptoetulips]

I agree with pp I also wouldn't Rush to use the tests up just make sure you have some back up if something comes back positive