What is better email performance worth to you?

A single headline number — "your email programme earns £X a month" — tells you nothing about where it comes from or what would move it. The result here is built step by step: sends, deliveries, opens, clicks, conversions, revenue, each line carrying the assumption that produced it. You know exactly which input to test, and what the change is worth.

The improvement section works the same way. Each rate — open, click, conversion — is tested alone, because rates interact: an open-rate gain and a conversion-rate gain don't stack the way adding their totals suggests. Testing levers in isolation keeps the arithmetic honest about what any single improvement is actually worth at your numbers.

One assumption is kept deliberately separate from the rest: bounce rate. Mail that never arrives is as much a list-hygiene matter as a campaign-performance one, and the calculator therefore doesn't fold it into the improvement maths where it would flatter the numbers. Dead addresses and list hygiene covers what to prune and when; what each bounce type costs you breaks down the signals behind your bounce rate. Before your next send, the preflight checklist catches the campaign-side faults that cost you money.