I used to work somewhere that did the forecast in a Google Sheet that lived in a folder called "OLD - Forecasting (2)" and everyone was pretty sure that wasn't the right file but no one wanted to be the person who asked.
That's not a joke. That's a real thing that happened in a real company with real investors looking at those numbers.
A forecast isn't just a number. It's a signal of how well your revenue system actually worrks. When a forecast is consistently accurate, it means your CRM data is clean, your reps understand their pipeline, and someone is holding the whole thing together with a consistent methodology. When it's consistently wrong, one of those three things is broken — and usually it's all three.
The monthly forecast SOP is about standardization more than anything else. Commit, Best Case, Pipeline — defined the same way, built the same way, reviewed the same way, every single month. The goal isn't a perfect number. The goal is a number you can learn from, because you built it the same way you built last month's.
Forecast accuracy is a lagging metric. It tells you how well your process worked. Run the process consistently for six months and you'll start to see patterns — which reps over-commit, which deals in which stages actually close, where your assumptions are off. That's the real value.
The forecast is the output. The process is the product.