Hi, it is difficult to give absolute figures as there are so many factors involved, however we do know the sustained release tablet format makes the B12 available for absorption over a 4-8 period, which gives the body a very good chance to absorb the vast majority of it. B12 is highly water-soluble and so the body takes what it requires with the rest safety excreted. Our current bottles are a sugar cane compound that is 100% biodegradable within 10 years.