How much blood can a person donate at one time and how long before major surgery you it?

The amount of blood that a person can donate at one time varies depending on their age, weight, and medical history. In general, a healthy adult can donate up to one pint (450 milliliters) of blood every 8 weeks.

It is important to stop donating blood at least 56 days before any major surgery, as donating blood can cause a decrease in blood volume and red blood cell count, which can lead to complications during surgery.