You can donate blood, ask your doctor (insurance may not cover it), or use a simple at home test like this (Eldoncard Blood Type Test (Complete Kit) - Air Sealed Envelope, Safety Lancet, Micropipette, Cleansing Swab https://smile.amazon.com/dp/B00JFTSPMW/ref=cm_sw_r_cp_api_i_...).

I used one of the card tests and got an O- result, then when I had annual bloodwork done I asked my doctor to test it just because an O- result on the cards looks the same as a possibly defective card (card wasn’t defective, I did in fact beat the 25% odds and inherited the negative Rh factor from both my O+ parents).

Donate blood, they'll tell you. The test is pretty simple and you can get home testing kits online if you want to do that instead; but giving blood helps other people too.

It's a common "experiment" run in high school science classes. It can be done with very little equipment (just a disposable lancet to prick the skin, and a disposable card to give you the results), and lends itself to interesting lessons on genetics, antibodies, etc.

Dangerous experiment. Must have found at least a few illegitimate children, if it is done routinely.

That's assuming the students know their parents' blood types with high confidence.

You can do a test at home using an "Eldon" kit. I did it this past weekend and it was pretty easy (other than getting the blood out). You get these special cards with reagents on that react with type A and type B blood as well as Rh+ and -, then the combination of the reactions tells you the blood type. In my case it was very obvious as the blood on the "anti B" card went very clotted whereas on the "anti A" card it was very smooth, placing me as type A.

Yes there exists simple tests to figure out your bloodtype.

Where I live, they specify blood type on your passport, driving license etc. So to obtain one you need to provide proof of your bloodtype.

Had to go to a lab to get that proof.

The test itself is pretty cheap and takes 5 minutes at most. They prick your hand, take a drop of blood, and do something with that (mix it with some other chemical or something).

Check your birth cert and passport. I believe some nationalities put blood type in these.

If you donate blood to, say, the Red Cross, then you'll be told your blood type.

Your mother will probably know. Mothers and babies are normally typed to avoid risk of this on subsequent pregnancies: https://en.wikipedia.org/wiki/Rh_disease