One six-thousandth or 0.016437322%

This is based on your birth weight being 3.5kg, your present weight being 80kg and 10% of your body mass being completely replaced with new material every year. It doesn't take into account that some atoms have different masses and that some elements (e.g. iron) are recycled in your body a lot faster than others (e.g. calcium).

It's probably very conservative to guess that 10% of your body mass is replaced with new material each year. The real answer is probably less than 0.01%.

The percentage would be fairly small. I can't imagine it would be only a fraction of a percent.

I would think most would be in your bones.