How likely would 4 pregnancy tests would be false negative?

Simple math problem that even I can do — with a caveat!

If each test has a 5% false negative rate, about 1 in 160,000.

If each test has a 1% false negative rate, about 1 in 100 million.

However, that caveat is that in real life errors are frequently correlated. So if there is something hormonally odd going on, you could still be pregnant and all simple tests could return negative every time.