IME, the only "test coverage % rule" that I've ever seen work was "must not decrease the overall percentage of tested code". Once you get to 100%, that becomes "All code must have a test".
Various people objected to this, pointing out that 100% test coverage tells you nothing about whether the tests are any good. Our lead (wisely, IMO) responded that they were correct - 100% tells you nothing - but that _any other percentage_ does tell you something.
Various people objected to this, pointing out that 100% test coverage tells you nothing about whether the tests are any good. Our lead (wisely, IMO) responded that they were correct - 100% tells you nothing - but that _any other percentage_ does tell you something.