How to Calculate Poisson Probability with POISSON.DIST in Excel

Use POISSON.DIST to model arrivals per time period — calls, customers, tickets — and plan capacity.

You will learn to

• Find the probability of exactly k arrivals
• Find the chance demand exceeds capacity
• Rescale the average rate for a different time window

How it works

POISSON.DIST models how many events happen in a fixed window of time when they arrive randomly at a steady average rate: calls per 10 minutes, customers per hour, support tickets per day. You only need the average.

With cumulative FALSE it returns the chance of exactly x events; with TRUE, x or fewer. For overload risk use 1 minus the cumulative probability of your capacity. If the window changes, scale the average first — 6 calls per 10 minutes is 3 per 5 minutes.

=POISSON.DIST(4,6,FALSE)