Biology
How many cells does your body replace each day?
Your body replaces roughly 330 billion cells a day, about 1% of the total, most of them blood and gut cells. Some, like the neurons of the cortex, are never replaced.
Source: Sender & Milo (2021), Nature Medicine.
Context
About 330 billion, around 1% of all your cells, according to Sender and Milo's 2021 accounting. Most of the turnover is blood cells and the lining of the gut, which wear out fast.
Some cells are never replaced. The neurons of the cerebral cortex you have now are, for the most part, the ones you were born with. The "new body every seven years" line is a myth; some tissues renew in days and others not at all.
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