How to Find a Value from a Probability with NORM.INV in Excel

Turn a target percentage into a real number with NORM.INV — perfect for delivery promises and cut-off times.

You will learn to

• Find the value that a given share of results stays under
• Find a cut-off for the fastest results
• Turn an upper-tail target into a cut-off

How it works

NORM.INV works backwards from NORM.DIST. Instead of asking "what share of deliveries take under 50 minutes?", you ask "how many minutes do 95% of deliveries take or less?" Give it the probability, the mean and the standard deviation and it returns the matching value.

This is ideal for setting promises and thresholds: delivery windows, warranty periods, grade boundaries. For an upper-tail target such as "only 2% may be late", pass 1 minus that share: =NORM.INV(1-2%,mean,sd).

=NORM.INV(0.95,42,9)