How to Calculate Marketing ROI

Don't let anyone tell you that calculating marketing ROI is some dark art. It’s not. In fact, stripping it back to basics, the formula is refreshingly simple.

At its core, here’s what you need:

ROI = (Sales Growth – Marketing Cost) / Marketing Cost

This gives you a ratio. To see it as a percentage, which is often easier to report on, just multiply that number by 100 .

That formula looks simple enough, doesn't it? The real trick, and where many businesses go wrong, is knowing exactly what numbers to plug in. Get this part wrong, and your final figure will be misleading at best.

The first mistake people make is only looking at their ad spend or the agency's monthly invoice. A true marketing cost includes everything that contributes to the effort. If you don't, you'll end up with an inflated ROI that doesn't reflect the real investment.

For an accurate picture, make sure you’re factoring in:

• Agency Fees: The retainer or project fees you're paying.
• Ad Spend: Your actual budget on platforms like Google Ads, Meta or LinkedIn.
• Software & Tools: The monthly subscriptions for your SEO tools, email platform, social media schedulers and analytics software.
• Content Creation: Any costs for freelance writers, photographers, video editors or designers.
• Internal Team Time: This one gets missed a lot. Calculate the salaried time your own team spends on marketing-related tasks, like managing the agency, attending meetings and reviewing work.

Being brutally honest with these costs is the only way to hold your marketing investment properly accountable.

Next up is sales growth. How much of your revenue can you genuinely attribute to your marketing? For some channels like PPC, this can be quite direct. For others, like organic SEO or a big digital PR campaign, it’s a bit less clear-cut.

For this basic formula, the simplest method is to compare a defined campaign period to a baseline period just before it started. If your revenue jumped by £50,000 in the quarter you launched a new campaign where you spent £10,000 , you’ve got the two figures you need.

This kind of top-level view is essential. With the UK digital agency market now a £20.4 billion industry, you have to know if your slice of that spend is working. Research shows that for every £1 spent on marketing, mid-sized firms see an average return of £4.11 . So, that £10,000 investment should ideally be bringing in around £41,100 in new revenue to be considered on par.

We have more on sophisticated attribution models and other insights on the Compare.Agency blog.

To get you started, here's a quick checklist of the data you'll need to pull together.

Gathering this information upfront makes the calculation itself a simple, five-minute job.

Any ROI calculation is only as reliable as the numbers you put into it. It’s a classic mistake to only count the most obvious costs, like your Google Ads budget or the agency’s monthly invoice. Doing this will almost certainly give you a rosier picture of your performance, which might feel good for a moment but is useless for making smart business decisions.

To get a figure you can actually trust, you need to track every single penny. I always advise clients to have one central place for all marketing expenditure—a simple spreadsheet is perfect for this. Getting your costs right isn't just a box-ticking exercise; it’s fundamental to understanding what’s really working.

First, let's get the easy stuff out of the way. These are the direct, tangible expenses you can pull straight from your invoices and bank statements. There’s really no excuse for missing these.

• Agency Fees: This is the monthly retainer or total project cost you pay your marketing agency.
• Ad Spend: The actual cash you’re spending on platforms like Google Ads , Meta (for Facebook and Instagram), LinkedIn Ads and TikTok.
• Software and Tools: Those monthly subscriptions add up surprisingly fast. Make sure you include your SEO tools ( Semrush , Ahrefs ), your email platform ( Mailchimp , Klaviyo ), social media schedulers and your CRM.
• Content and Creative: Any costs for freelance writers, photographers, video production or graphic designers.

Most businesses are pretty good at tracking these line items. But if you stop here, you're only seeing half the story.

This is where I see most ROI calculations fall apart. These less obvious costs are harder to pin down, but they are just as real. Ignoring them is like trying to weigh yourself but conveniently forgetting about your heavy boots and winter coat.

To get a true picture, you have to be honest about these internal expenses:

• Internal Staff Time: Work out the portion of salaries for any team members involved in marketing. This includes time spent reviewing creative, approving content or sitting in on campaign meetings. A rough percentage based on their weekly hours is a great starting point.
• Training and Development: Have you sent anyone on a course to get better at marketing or managing your agency? That's a marketing cost.
• One-Off Project Costs: Think about expenses like hiring a stand at a trade show or printing brochures that support a digital campaign.

By diligently tracking both direct and hidden costs in one place, you build a completely accurate 'Total Marketing Cost' figure. This makes your monthly and quarterly ROI checks faster, more reliable and far more useful for judging whether your investment is actually paying off.

Alright, let's get into the tricky part. A customer might see a Facebook ad, Google your brand name, read a couple of blog posts and then finally make a purchase after clicking a link in an email. So, which channel gets the credit? Who gets to claim the glory in their monthly report?

This is the central problem of marketing attribution. It’s the process of assigning value to the marketing touchpoints that influence a customer's decision to buy. Getting this right—or at least understanding the biases of the method you choose—is crucial for an accurate ROI calculation. If you get it wrong, you could end up pouring money into channels that look good on paper but aren't actually driving the business forward.

Last-touch attribution is the default setting for many analytics tools, mainly because it’s the simplest to track. It gives 100% of the credit for a sale to the very last interaction the customer had before converting. If they clicked a Google Ad and bought something, Google Ads gets all the praise.

This model is popular because it’s so straightforward. The problem? It’s like giving all the credit for a goal to the striker who tapped it in from a foot out, completely ignoring the midfielder who ran the length of the pitch to set it up. Last-touch heavily favours channels that capture existing demand, like branded search or retargeting ads, while undervaluing the channels that created that demand in the first place.

On the flip side, you have first-touch attribution. This model gives 100% of the credit to the very first marketing interaction a customer had with your brand. If they initially discovered you through a blog post they found via organic search and then converted three weeks later, your SEO efforts get to take a victory lap.

This approach is handy for understanding which channels are good at introducing new people to your brand. Its major flaw, however, is that it completely ignores everything that happened afterwards to convince that person to actually part with their cash. It tells you who started the conversation but gives you no clue as to who closed the deal.

A much more balanced view comes from multi-touch attribution. Instead of giving all the credit to a single interaction, it spreads the value across multiple touchpoints in the customer's journey. It’s more complex, but it paints a far more realistic picture.

There are a few common ways to slice it:

• Linear: This model gives equal credit to every single touchpoint. It's democratic, but it doesn't distinguish between a casual glance at a social post and a decisive click on a final offer.

• Time-Decay: This gives more credit to the interactions that happened closer to the sale. It rightly acknowledges that the final touchpoints are often more influential, but it doesn't completely ignore the earlier ones that started the journey.

• Position-Based (U-Shaped): This is a popular compromise and often a great starting point. It typically gives 40% of the credit to the first touch, 40% to the last touch (the conversion), and splits the remaining 20% among all the interactions in between.

A single, blended ROI figure for all your marketing is a decent starting point, but it doesn't tell you the whole story. It’s a bit like knowing the average temperature of a hospital is 37°C – it hides the fact that some patients are running a fever while others are perfectly fine. The real insight comes when you calculate ROI for each specific channel. That’s how you spot what’s truly driving growth and what’s just burning through your budget.

Figuring this out looks different depending on the marketing discipline. Some channels are pretty straightforward, while others demand a bit more patience and some smart estimation.

SEO is a long game, so you need a different mindset when measuring its return. You aren't paying for each click; you're typically paying an agency a monthly retainer to steadily improve your organic search visibility. The trick, then, is to assign a concrete value to the organic traffic they bring in.

A common and effective way to do this is to calculate what we call 'organic traffic value'. You can use popular SEO tools to see what you would have paid through Google Ads for the exact same clicks your organic rankings are now delivering. It’s a powerful way to frame the return.

PPC is far more direct, which makes the ROI calculation much cleaner. You spend money on ads, people click them and (with any luck) they make a purchase. The formula here is simple: revenue generated from the ads versus the total cost, which must include both the ad spend and any agency management fees.

This is where the attribution models we touched on earlier become critical. How you assign credit for a sale dramatically changes the outcome.

As you can see, 'First-Touch', 'Last-Touch' and 'Multi-Touch' models assign credit very differently. A PPC agency might naturally favour a last-touch model because it makes their campaigns, which often capture users at the point of purchase, look incredibly effective. However, a multi-touch view often gives a fairer, more balanced picture of the entire customer journey.

For years, email marketing has consistently delivered one of the highest returns in the business. This is largely down to its low operational cost and the direct line it provides to an audience that has already opted in. Calculating its ROI is usually straightforward: take the revenue from email campaigns and subtract the cost of your email platform and any content or agency fees.

It’s a channel where small optimisations often lead to big gains. It's projected that by 2026, UK email marketing could deliver an average return of £32 for every £1 spent . For a London based e-commerce brand spending £5,000 on a well executed campaign, a 32x return would mean £160,000 in new revenue. You can find more on how UK brands are achieving this in this 2025 marketing statistics report.

This is arguably the trickiest one of the lot. A blog post, a video or a downloadable guide rarely leads directly to a sale on the same day. Its true value often emerges over a much longer period, making its impact harder to pin down.

Content typically contributes to your bottom line in a few key ways:

• Lead Generation: A valuable guide or webinar captures an email address, which your sales or email marketing team can then nurture into a paying customer.
• Brand Authority: Over time, great content leads to more people searching for your brand by name and visiting your site directly. This shows you're building trust and becoming a go-to resource.
• Assisted Conversions: Content often plays a vital role early in the buying journey. It helps to educate and inform potential customers before another channel, like PPC or email, closes the deal.

Breaking down your numbers by channel stops you from making broad, unhelpful statements like 'our marketing is working'. Instead, it equips you to have pointed, data-led conversations with your agencies about what's performing, what isn't and where the next pound of your budget should be invested. For more on this, check out our other guides for UK businesses.

If you’re only looking at the profit from a customer's first purchase, you're getting a dangerously incomplete picture. I’ve seen it happen time and again: a business looks at a campaign, sees a low initial return and pulls the plug. They don't realise they’ve just shut down the very channel that was bringing in their most valuable long term customers.

A customer who spends £50 on their first order might go on to spend £500 over the next two years. Judging your marketing on that initial £50 is a classic, costly mistake.

This is where you need to get familiar with Customer Lifetime Value (LTV) . Simply put, it’s the total amount of money you can realistically expect to earn from a customer over the entire time they do business with you. When you factor LTV into your ROI, you move from short term thinking to a much more strategic view of what’s actually working.

For any business built on repeat custom – think subscription models, e-commerce stores or any service with loyal clients – ignoring LTV is like flying blind.

Getting a handle on your LTV doesn't require a team of data scientists. You can get a solid, workable estimate by pulling together three figures you likely already have somewhere in your business data.

Here's what you'll need to find:

• Average Order Value (AOV): How much does a customer typically spend in one go? To find it, just divide your total revenue over a period (say, a year) by the total number of orders in that same period.
• Purchase Frequency: On average, how many times does a customer buy from you in a year?
• Customer Lifespan: How long do people tend to stay customers? This can be an estimate, like two, three or five years.

With those numbers in hand, the calculation is straightforward.

Let's imagine your average customer spends £75 per order, buys from you three times a year and typically remains a customer for four years .

Their LTV would be £900 (£75 x 3 x 4). Suddenly, that single £75 purchase looks very different, doesn't it?

Now we can bring this LTV figure back to our original ROI formula to get a true sense of a campaign's long term profitability. This new calculation reveals the return on acquiring a customer , not just on securing a single sale.

The adjusted formula is:

LTV-Based ROI = (LTV – Marketing Cost) / Marketing Cost

Let’s see how this transforms our perspective. Say you spend £100 on a Google Ads campaign to acquire one new customer and their first purchase is £75 .

Using the basic formula, you’re in the red. Your ROI is a discouraging -25% . Based on this, you'd probably call the campaign a failure.

But when we bring in our LTV of £900 , the story completely flips:

(£900 LTV – £100 Marketing Cost) / £100 Marketing Cost = 8

Your ROI is now 8 , which translates to 800% . That 'failing' campaign is actually one of your most powerful long term investments. This is the kind of insight that changes how you allocate your budget and the conversations you have with your marketing agency.

So, you’ve got a handle on calculating your marketing ROI. That’s a huge step, but the real test is putting that knowledge to work. This is where you move from just tracking numbers to making genuinely smarter decisions, especially when hiring a marketing agency.

Armed with your own performance data, you can finally stop using vague briefs like 'we want to grow'. Instead, you can provide concrete targets and benchmarks. It fundamentally changes the conversation, forcing agencies to present realistic, data-backed forecasts rather than just impressive-sounding ideas.

When you sit down to write your next agency brief, be upfront with your numbers. Laying your cards on the table from the start sets a tone of transparency and accountability.

Here’s what I’d recommend including:

• Your current blended ROI: Share the overall picture of your marketing performance.
• Channel-specific ROI: Be specific. If you know your PPC campaigns are delivering a 3:1 return but your organic efforts are trailing, say so.
• Customer Lifetime Value (LTV): Including your LTV signals that you’re focused on sustainable, long term growth, not just quick, superficial wins.
• A clear target ROI: Give them a finish line to aim for. For instance, 'Our objective for this campaign is to achieve a minimum 4:1 ROI'.

This kind of detail is a fantastic filter. A great agency will relish the clarity and use it to build a credible, tailored strategy. Any agency that gets spooked by the prospect of being held accountable for results is probably one you’d want to avoid anyway.

Once the pitches start coming in, your understanding of ROI becomes your most powerful vetting tool. You can cut through the usual agency spiel about past clients and get to the heart of what matters: how they think about and manage your money.

To make sure you don't fall into that same trap, you need to ask pointed, ROI-centric questions. Try these during your next agency interview:

• 'Could you walk me through a sample report and explain the attribution model you used for that client?'
• 'What’s your standard procedure if a campaign’s ROI falls below our agreed target for two consecutive months?'
• 'How do you propose we calculate the return on the content marketing part of your proposal?'
• 'Given our LTV is £X, what Customer Acquisition Cost (CAC) would you see as a success for this campaign?'

Their responses—or lack thereof—will tell you everything. If they get flustered, can’t produce a clear report or give you a blank stare when you mention LTV, you know they aren’t the right partner for a results-driven business. For an even more comprehensive list, check out our guide on questions to ask a marketing agency.

This entire approach ensures you hire a partner who is just as invested in your bottom line as you are.