How Often After Donating Whole Blood Can I Donate Platelets? What About Plasma?

It takes about 8 weeks for your body to replenish all the blood cells removed after donating one unit of whole blood. That’s why you have to wait the 56 days. That time limit is for *any* subsequent donation. If you regularly donate plasma or platelets, you can donate every 7-14 days, depending on the blood center. But you have to wait until the first 56 days is up before you can donate the plasma/platelets. The time frame between donations is always started with the donation and counted forward depending on the type of donation, not counted backwards from the next donation. In other words, if you donate whole blood or red blood cells, you have to wait 56 days before donating any blood product, not “you can donate plasma if you haven’t donated any blood product in the last 7 days.”
As to which is needed more, both plasma and platelets are in high demand, as they are used for different things. But one thing to be aware of: the FDA (in the US) has placed restrictions on how plasma from females is used. Since any female who has ever been pregnant might have an antibody that can cause a severe reaction in a recipient. If you are female, whether you have been pregnant or not, your plasma will not be transfused directly into any patient. It will be used for research purposes or be made into testing reagents or for certain medications. If you are wanting to save lives directly, stick to whole blood or platelets. If you’re a guy, sorry, and you can disregard this.
Thanks for donating blood!

I believe that because you just gave whole blood, you have to wait 56 days to donate anything else.
AFTER THAT…
If you want to donate platelets, you can donate up to once every seven days. This is because just the platelets are removed, and then the rest of your blood is given back to you. Same with plasma. They’re both needed equally.

Wrong! I donate whole blood every 56 days and platelets in between. The National Institutes of Health requires you to wait two weeks after whole blood donation to donate platelets. Red blood cells take 2-4 weeks to replenish while platelets only take 72 hours, even after whole blood donation. Some places even allow you to donate platelets every 72 hours.
See: http://www.blood.ca/centreapps/internet/uw_v502_mainengine.nsf/page/donor+faqs?opendocument where it says:

2. How long does it take to replace the whole blood taken during donation?

The plasma portion of a donation is replaced within hours, the platelet portion within days and red blood cells in about 56 days. This is why blood donors cannot give more often than once every 56 days.