This app was mentioned in 6 comments, with an average of 4.83 upvotes
Speaking to my wife we have come up with this.
Missing one pill is unlikely to make you fall pregnant if you are on a regular dosage of them. But as we all know there is still a change of Pregnancy, Try adding a spermicidal lube when you have unprotected sex (if you don't use condoms) this can lower your risk even more of getting pregnant.
My wife has been a week late with her period, this is normally induced by having sex a day or two before it's due, but other times it has made it come early.
There is a chance that you could be pregnant, but again it's unlikely. If you are worried book in for a blood test they are even more accurate that the over the counter tests as early stages.
My wife recommends that you download and use regularly (more accurate that way) this app.
Glow:
APPLE: https://itunes.apple.com/us/app/glow-ovulation-calculator/id638021335?mt=8
ANDROID: https://play.google.com/store/apps/details?id=com.glow.android&hl=en
Good luck, and if in doubt use protection as there is always a chance :) edit: spelling.
You can try Glow. They have two different type of apps for different kinds of ppl. Glow for more serious, and eve for more fun.
If you are using an Android phone, you can download it at https://play.google.com/store/apps/details?id=com.glow.android and https://play.google.com/store/apps/details?id=com.glow.android.eve.
If you are using an iPhone, you can find it by search Glow or Eve.
I use Glow because it can be used to track ovulation (fertile time frames) and pregnancies as well. totally not pink, no flowers.
https://play.google.com/store/apps/details?id=com.glow.android
edit: you can also put details on when you had sex, whatever physical stuff (headache, bloating, fatigue etc) you're feeling and other stuff about your emotions if you're into that.
My boyfriend and I use Glow. It's pretty accurate, so long as you feed it enough data to work with.
Glow is also fantastic!