Why We Built An ROI Calculator
Marketers are surrounded by metrics, but the real question is simple:
"If I change this one thing in my campaign, what actually happens to my money?"
That gap between numbers and clarity is why we built our own ROI calculator. Not as a perfect financial model, but as a quick way to see how a campaign hangs together and where it might quietly fall apart.
We used AI, a spreadsheet and a whiteboard in the office to map what really matters: how budget, clicks, conversions and value connect. The result is a top line tool that shows how we think and approach performance problems.
A Simple Way To See The Whole Story
The calculator asks for a handful of inputs you already talk about every day:
Media budget
Click through rate and cost per click
Conversion rate
Average order value and basic margin
Simple repeat purchase behaviour
From that, it gives you a rough view of:
Impressions, clicks and conversions
CPA and ROAS
Revenue and profit at a high level
The insight is not that the numbers are perfect. It is that you can instantly see how sensitive your plan is. Nudge CTR down a little. Make conversion more realistic. Lift AOV slightly. You feel the whole funnel react.
It turns vague optimism into visible trade offs.
A Teaser, Not A Full Financial Model
It is important to be honest about what this tool is.
It is not a full P&L. It will not replace client specific modelling or detailed forecasting across markets and product lines.
It is a top line teaser:
A way to visualise how a plan might behave
A way to stress test heroic assumptions
A way to frame the right questions before you spend
In other words, it is there to sharpen thinking, not to tick off a finance checklist.
How We Use It In Practice
Inside One Day, the calculator has become a useful prop in real conversations. We use it to:
Sanity check early ideas before they make a deck
Sense check whether targets match the budget on the table
Walk clients through "is this really profitable?" in a clear, non-technical way
Instead of debating in abstract, we drop in rough numbers and explore scenarios live. It quickly shows whether a plan relies on unrealistic performance, or where a small improvement could unlock real profit.
The most valuable part is often not the output, but the discussion it triggers:
Why do we believe this conversion rate?
What would it take to increase AOV?
Are we comfortable with this payback picture?
Try It For Your Own Numbers
If you want to see how your own assumptions hold up, you can try the calculator here:
https://oneday.agency/roi-calculator
Final Thought
In a noisy performance world, tools that force clearer thinking are more useful than tools that claim perfect answers.
A simple ROI calculator will not solve your strategy, but it will make your assumptions visible. When you can see how each lever affects the outcome, you are already making better decisions, as we do at One Day.
