We built a SaaS Retention Calculator so you don't have to

Ask any SaaS founder, product manager, or growth marketer what keeps them up at night, and one word tends to echo back louder than most: churn.

You can have the slickest onboarding, a killer acquisition campaign, and an amazing engineering team... but if users quietly drop off after a few weeks or months, all of that effort turns into a leaky bucket.

Retention isn’t just a KPI – it’s a survival metric. And yet, it’s often the least tangible and least budgeted part of the SaaS journey. We’ve sat in enough meetings to hear variations of the same frustrating question:

“Do we really need to invest more in UX? Can’t we just fix churn with a few more emails?”

That’s when we knew we needed to build something better than words or generic dashboards. Something that would speak the language of revenue, forecasts, and ROI – and make the case for UX improvements using logic that even the most numbers-obsessed CFO couldn’t ignore.

So we created a tool: a Custom SaaS Retention & UX ROI Calculator that helps quantify the business case for product improvements. Here's how we built it – and why it matters.

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Ever tried convincing your CEO that fixing your product’s UX isn’t just “nice to have”?

That it’s not just about “prettier buttons,” but about retention, LTV, and actual money in the bank?

Well, we got tired of waving hands in meetings too. So we built a thing:

A Custom SaaS Retention & UX ROI Calculator that makes the financial case for improving product experience — with actual numbers your board will love.

The Problem: Churn Is a Silent Killer

Let’s face it – acquisition gets the spotlight, but churn quietly eats away at everything you’ve built. It’s not glamorous, but it’s powerful. And too often, it’s ignored.

Most SaaS teams track churn – but few model the downstream financial impact of small improvements. A couple of percentage points off your churn rate can be the difference between scraping by and scaling sustainably.

In our sample scenario, the product team faced:

• 22% churn
• A monthly LTV of just $109
• A CAC of $80 and a payback period of 3.3 months

With numbers like that, you're barely breaking even on acquisition. You can keep throwing cash at performance marketing – or you can fix the leaks in your product experience.

👇 Here’s what that looked like inside the tool:

With numbers like that, you’re barely breaking even on acquisition. Sure, you can throw more cash at paid ads to refill the funnel.

Or... you could fix the leaks in your bucket.

The Idea: Making Retention Tangible for Everyone

Retention is tricky. It’s not a single feature or flow – it’s the cumulative effect of a user’s experience over time. That makes it hard to argue for, especially when competing with feature requests, acquisition goals, and investor asks.

We realised that while teams felt the pain of churn, they couldn’t always see the payoff of investing in UX. What they needed wasn’t another presentation. They needed a way to see the upside – in numbers.

So we built a simple calculator. You enter your current metrics – monthly active users, retention rate, average revenue per user, acquisition cost. Then, you estimate the potential retention uplift from a UX improvement.

That’s it. The calculator does the rest – projecting revenue, ROI, and user retention across the next 12 months.

What the Calculator Shows You (in Seconds)

No need to fiddle with spreadsheets. Once you enter your current metrics, the calculator simulates what happens if you improve retention – even slightly.

You get a clear forecast including:

• 12-month revenue impact
• The break-even timeline on your UX investment
• Additional retained users and LTV growth
• ROI per $1 spent

In one example:

• $12,500 investment in UX
• 1-month implementation time
• +4% retention uplift
• Break-even reached in 4.7 months
• $31,705 in additional revenue across the year

We intentionally kept the interface lightweight – just enough structure to guide you, but flexible enough for teams of different shapes and sizes.

A Closer Look at Real-World Scenarios

We were curious to test how different team profiles would use this. Turns out, the tool helped uncover overlooked ROI in several contexts:

• Startups testing pricing changes – now able to model retention effects
• Mid-stage SaaS teams struggling with activation drop-offs – using it to justify onboarding UX tweaks
• Growth marketers – leveraging ROI models to support lifecycle campaigns

Small retention gains can lead to significant long-term value. More importantly, these forecasts are easy to understand and easy to present to stakeholders who care about outcomes more than UX theory.

Why Marketing and Product Teams Both Love It

Though we built it with product managers in mind, marketers quickly became some of our biggest users.

That’s because retention isn’t just a product issue – it’s a growth issue. When churn goes down:

• LTV increases
• Paid acquisition becomes more efficient
• User satisfaction improves – which boosts referrals

Marketers use the calculator to justify CRO experiments, onboarding emails, or even campaign budget reallocation. Product teams use it to support design decisions, UX audits, and roadmap planning.

In both cases, the tool offers a shared language – revenue.

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If you’re trying to grow your SaaS business, don’t just look at the top of the funnel. Sometimes, the biggest gains come from the users you already have.

We created this calculator as a way to make retention visible – not as a vague concept, but as a set of clear financial outcomes. It helps teams argue for better UX and smarter design investments using logic that anyone can appreciate.

And if you ever find yourself struggling to explain why retention matters, remember:

“The best growth hack is keeping the customers you already paid for.”

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Built with love (and churn math), The DNSK WORK team, London 2025

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P.S. If you’re curious, we’ll open-source a stripped version of the calculator soon. Follow us for updates.