This series argues that the best impact stories are built on maths. So far we looked at a training programme that pays for itself if people become 0.2% more effective, an onboarding portal that recovers its cost in advisor time within a year, and a compliance programme that justifies itself by preventing one serious incident every few years.

The financial logic is the same each time. Examine multiple layers of consequence to find the number your audience cares about. Show the threshold. Make the bar feel obvious.

And societal impact is no different.

The impact of a clean floor

Last year, I coached a cohort of sustainability start-ups on an incubator programme. One of them had developed a natural compound to upgrade homes and schools from dirt floors to clean, durable surfaces. Operating across Rwanda, Uganda and Kenya. The floor cost $2 per square metre; a typical home is 25 square metres, so $50 gives a home a clean floor.

The immediate impact is obvious. Cleaner floors mean fewer parasites, less diarrhoea, fewer skin and respiratory infections. 93% of parents whose children attended early childhood centres with this new flooring reported their children were healthier afterwards.

So there’s your primary impact - health.

The cascade

A rural village of 200 households would be a population of around a thousand people, 400 of them children.

The entire village gets new floors at a total investment of $10,000.

Now follow what happens next.

Health centre savings. Assume each household makes four fewer clinic visits a year, a conservative estimate given what the parents are reporting. The government in Rwanda covers around 90% of each visit, paying roughly $30 per patient. Four fewer visits each from two hundred households equates to $24,000 saved by the healthcare system every year.

The $10,000 investment pays for itself in five months from healthcare savings alone.

School attendance. Imagine two children per household each missing three fewer sick days a year. That’s 1,200 school days recovered across the village annually. These are days children get back in school instead of stuck at home with an upset tummy.

Parental working days. Assume half those sick days required a parent to stay home. Now we’ve also recovered six hundred working days. At a rural daily wage of $3, that’s $1,800 back into the community each year.

A new trade. The flooring system requires trained installers, masons, as they’re known locally. Say in a village of 200 homes, one person might train up as a mason. A mason earning the installation rate and working steadily generates roughly $2,500 a year. Against a rural agricultural wage of around $750, that’s a net income uplift of $1,750 per Mason.

Aggregation: the next level of the cascade

Beyond the $240,000 in cumulative healthcare savings over ten years, which already justifies the original investment twenty-four times over, the cascade delivers a further $35,500 in quantifiable community value over that time in restored parental earnings and new mason income, compounded over a decade.

On top of a $10,000 investment.

I’ve left the school days unmonetised deliberately. Putting a price on children’s education feels like a step too far. The 12,000 school days over ten years speaks for itself.

And what else the model doesn’t capture

Money that stays in a community doesn’t sit still. The mason spends his or her income at the local market. The parent who didn’t lose three days’ wages buys better food, or a cooking stove, or a bicycle. Which sounds trivial until you realise a bicycle means access to work two villages away. Which means more income. Which means more choices.

Economists call this the multiplier effect. I’d call it the point where Impact Storytelling reaches its limit, not because the impact stops, but because it becomes difficult to follow every thread.

That’s the strength in the argument. Societal impact, unlike financial or efficiency impact, has no ceiling. An organisation that reduces its costs eventually reaches a floor. A community that becomes healthier, better educated and more economically active (in this case, with clean floors) keeps compounding, and the cascade never fully stops.

Show your working

Every number in this model is an assumption. I’ve been transparent about that throughout. Four fewer clinic visits per household, three fewer sick days per child, half requiring a parent to stay home, $3 daily rural wage, all these numbers are educated guesses or conservative estimates. When you can’t claim precision, you can invite your audience to stress-test the logic. And it’s all the more credible when you don’t exaggerate.

Do these assumptions feel plausible? If they do, and I think they do, the conclusion follows.

Showing the working, making the bar visible, letting your audience decide whether they believe the threshold is achievable: that’s what this series has been about throughout. Societal impact is where it matters most, because the numbers you can’t audit are working hardest.

A method you can use

1. If you’re building a societal impact case, here’s the approach:

2. Start with the primary impact: the most direct, most measurable effect of your intervention.

3. Map the cascade: what does that primary impact lead to, and what does each of those lead to in turn?

4. Quantify what you can, using conservative and transparent assumptions.

5. Leave what you can’t quantify unmonetised, but still call it out.

6. Show the multiplier effect as a qualitative argument once the numbers have done their work.

7. Invite your audience to stress-test the assumptions, not accept them.

The cascade is the story. You follow it through far enough that the cumulative logic becomes hard to argue with, then let the reader take it the rest of the way.

Your turn

Where are you struggling to make a societal impact case? Is it the data, the assumptions, or the audience: a funder, a government, a board that wants proof you can’t provide?

Would love to hear how you make the case. What have I missed?

I spent twenty years in senior leadership roles at Sky, ITV, NBC News and Future Plc before becoming a Consulting Partner at Positive Momentum, where I advise organisations across financial services, sustainability and technology on strategy, storytelling and change. Impact Storytelling sits at the centre of that work.