A human cell has about 3 billion base pairs of DNA (p. 26), for a total of 6 billion nucleotides.
DNA replication is 99.99999999% accurate, and yields 1 mutation per 10 billion nucleotides.
Therefore, each cell division yields about 0.6 mutation.
Your average cell has divided about 47 times from a single zygote.
After 47 divisions, your average somatic cell has accumulated about 28 mutations.
You have 100 trillion (1014) somatic cells (p. 15).
You have a total of 2,800 trillion, or 2.8 quadrillion (2.8 x 1015) mutations in your cells, not counting gametes.