Work out capacity headroom instantly with clear inputs, formula shown and shareable results.
Capacity runs out on a compound curve, so headroom in months is the logarithm of the ratio between the safe ceiling and current utilisation, divided by the log of the growth factor. What turns that into an action is procurement lead time: if capacity takes six weeks to arrive, the order must be placed six weeks before the ceiling is reached, not when it is hit.
Headroom timing
months = ln(max safe / current) / ln(1 + monthly growth); order deadline = months - lead time in months
Queueing delay grows sharply above that, and headroom is needed to absorb a failed replica or an unexpected burst. The exact number depends on how spiky the workload is.
It shortens lead time but does not eliminate it. Quotas, instance-type availability and stateful services all have their own lead times.