Solved: How Long Should Ads Run Before Changing?

Hi there,

Thanks for reaching out! Happy to give you some initial thoughts and guidance on your advertising question. That "50 conversions" rule you mentioned is one of those things that sounds official but can be really misleading in practice. The truth is, you can often spot a winning or losing ad far sooner than that, and knowing what to look for is what seperates a profitable campaign from a money pit.

I'll walk you through a more reliable framework for making these decisions, from understanding the real metrics that matter to knowing what you can actually afford to spend to get a customer. It's less about magic numbers and more about understanding your own business economics.

We'll need to look at why that "50 conversions" rule is a bit of a trap...

Right, let's get this one out of the way first. The advice from ChatGPT to wait for 50 conversions before making a decision comes directly from the ad platforms themselves, mainly Meta (Facebook/Instagram). They call this the 'learning phase'. The idea is that their algorithm needs this much data to understand who your ideal customer is and how to find more of them efficiently. In a perfect world, with an unlimited budget, this is fine advice. But for most businesses, it's a recipe for burning cash.

The problem is, the algorithm doesn't care about your profit margins. It only cares about hitting the objective you gave it (e.g., "get conversions") at the lowest possible cost *it can find*. It has no concept of whether a £100 cost per conversion will bankrupt you if you're selling a £50 product. It'll happily spend your entire budget trying to get to 50 conversions, even if every single one is a loss.

Imagine you're selling handcrafted jewelry for £75. After 5 conversions, you've spent £400. That's a CPA of £80 per sale. You're already losing money on every single sale. Do you really need to wait for another 45 loss-making conversions to confirm what the data is already screaming at you? Of course not. The algorithm isn't going to magically slash your CPA by 80% overnight. Small improvements are possible, but dramatic shifts like that are rare once a pattern has been established.

We see this all the time. A client comes to us after being told to "trust the process" and let the learning phase complete, but they've just spent £2,000 to generate £500 in revenue. They know somethings wrong, but they're afraid to intervene because they've been told not to. The reality is, you need to be an active manager of your campaigns, not a passive observer. You should be looking for early indicators of success or failure. If an ad isn't showing promise within a reasonable timeframe (which we'll define next), it's far better to kill it and test something new than to let it bleed your budget dry in the hope of a miracle.

I remember one e-commerce client selling cleaning products. Their initial ads were getting a CPA of around £40, but their average order value was only £30. They'd been told to let it run. We came in, looked at the numbers after just a day or two, and could see the fundamental economics were broken. We paused those ads immediately, reworked the creative and targeting, and got the CPA down to under £10. They eventually achieved a 633% return. Had they waited for 50 conversions on the original ads, they would've been out of business.

I'd say you should focus on these early warning signs instead...

So, if the 50-conversion mark is unreliable, what should you be looking at? You need a simple decision-making framework based on profitability and leading indicators. It's about knowing your numbers and having the confidence to act on them quickly. Here are the key things to watch.

1. Your Break-Even CPA (Cost Per Acquisition)
This is the absolute most you can spend to acquire a customer and not lose money. If you sell a product for £100 and your cost to produce and deliver it is £40, your profit is £60. Your break-even CPA is £60. Any ad that brings in a customer for less than £60 is profitable. Any ad that costs more is a loss. You need to know this number *before* you spend a single penny. Your goal is to get your CPA as far below this number as possible.

2. The "3x CPA" Spend Rule
This is a much better rule of thumb than the 50 conversions one. Once an ad set has spent 2x to 3x your *target* CPA without a single conversion, it's probably a dud. For example, if your target CPA is £20, and an ad set has spent £60 without a single sale, the odds of it suddenly becoming a profitable performer are very, very low. It's time to pause it and re-evaluate. Why keep betting on a losing horse?

3. Leading Indicators: CTR and CPC
Sometimes you can spot a problem even before the CPA data comes in. The Click-Through Rate (CTR) and Cost Per Click (CPC) are your canaries in the coal mine.

-> Click-Through Rate (CTR): This is the percentage of people who see your ad and click on it. A very low CTR (e.g., below 0.5% on Meta) tells you the ad isn't resonating with the audience. The image might be poor, the copy might be weak, or the offer might be irrelevant. The ad isn't grabbing attention.

-> Cost Per Click (CPC): This is what you pay for each click. If your CPC is sky-high, it's often because your CTR is low (the platform charges you more if users don't engage with your ad) or because you're in a very competitive auction. If your CPC is £5 and you need a 2% conversion rate on your website to be profitable, your CPA will be a staggering £250 (£5 / 2%). If that's not sustainable, you know you have a problem right at the click stage.

By monitoring these metrics, you can diagnose problems early. Low CTR? The ad creative or targeting is the problem. High CPC but good CTR? You're likely in a very competitive audience. Clicks are cheap and CTR is high, but no conversions? The problem is almost definately on your landing page or with your offer.

To make this easier, here is a simple flowchart that maps out the decision-making process. It's a much more practical way to think about ad management than just waiting for a magic number.

You probably should calculate your Customer Lifetime Value (LTV)...

Now we get to the most important metric that most businesses completely ignore: Customer Lifetime Value (LTV). Knowing this number changes everything. It shifts your entire mindset from "How little can I spend?" to "How much can I *afford* to spend to beat my competition?".

The LTV is the total profit you can expect to make from a single customer over the entire duration of their relationship with you. Why is this so powerful? Because it tells you the true value of an acquisition. You might lose money on the *first* sale, but if that customer comes back and buys from you five more times, you've made a huge profit. Businesses that understand their LTV can afford to pay much more to acquire a customer, allowing them to scale aggressively while their competitors are stuck trying to make a profit on every single transaction.

Let's take a B2B SaaS company as an example. Their CPA might be £500, which sounds huge. But if they know that the average customer stays for 36 months paying £200 a month, their LTV is enormous, making that £500 acquisition cost a brilliant investment. We worked with a medical job matching SaaS that initially had a CPA of £100. They thought this was too high. But after we analysed their LTV, we realised they could comfortably afford to spend much more. This insight allowed us to scale their campaigns on Meta and Google, and we ultimately reduced their CPA to just £7 while massively increasing their user base.

Calculating a basic LTV isn't as complicated as it sounds. Here’s a simple formula for a subscription-based business:

LTV = (Average Revenue Per Customer Per Month × Gross Margin %) / Monthly Customer Churn Rate

Let's break that down:

-> Average Revenue Per Customer (ARPA): Simple enough. What's the average amount a customer pays you each month?

-> Gross Margin %: What's your profit on that revenue? If you charge £100 and your costs to service that customer are £20, your gross margin is 80%.

-> Monthly Churn Rate: What percentage of your customers cancel their subscription each month? If you lose 5 out of every 100 customers, your churn rate is 5%.

For an e-commerce business, the calculation is a bit different. You'd calculate it as: (Average Order Value × Purchase Frequency × Gross Margin %) × Average Customer Lifespan.

Once you have your LTV, you can determine your maximum allowable Customer Acquisition Cost (CAC). A healthy ratio for a growing business is often cited as 3:1 (LTV:CAC). This means if your LTV is £9,000, you can afford to spend up to £3,000 to acquire that customer. This completely reframes how you look at your ad spend. A £200 CPL from a LinkedIn campaign doesn't seem so scary when you know it leads to a £9,000 customer.

To make this tangible for you, I've built a little interactive calculator below. Play around with the numbers for your own business. See how a small improvement in customer retention (lower churn) or a slight increase in your monthly fee can dramatically increase your LTV, giving you more firepower for your advertising.

You'll need a proper testing structure...

Going with "trial and error" is another way of saying "setting money on fire". A structured approach to testing is essential. Instead of randomly trying different things, you need a logical system that tests the most likely-to-succeed elements first and expands from there. This saves you time, money, and a lot of frustration.

The core idea is to structure your campaigns based on the marketing funnel: Top of Funnel (ToFu), Middle of Funnel (MoFu), and Bottom of Funnel (BoFu). These represent different stages of customer awareness.

-> Top of Funnel (ToFu): Cold Audiences. These are people who have never heard of you before. This is where you'll use interest-based targeting, demographic targeting, or broad targeting (once your account has enough data). This is the largest and usually the most expensive part of the funnel to get conversions from.

-> Middle of Funnel (MoFu): Warm Audiences. These are people who have shown some interest but haven't taken a key action yet. This includes people who have watched your videos, engaged with your social media posts, or visited your website but didn't add anything to the cart.

-> Bottom of Funnel (BoFu): Hot Audiences. These are people on the verge of converting. They've added a product to their cart, initiated checkout, or repeatedly visited a key page. This is your lowest-hanging fruit and should almost always be your most profitable audience.

Your testing priority should always be from the bottom of the funnel upwards. Why? Because BoFu audiences are the most likely to convert. They already know you and have shown strong intent. Proving your ads can work with this audience first gives you a profitable foundation. Then you can move up to MoFu, and finally, scale with ToFu audiences.

Here's how I would prioritise audience testing within a Meta ads account, assuming an e-commerce store. The principle is the same for nearly any business type.

When you start a new account, you won't have data for BoFu or MoFu audiences, so you have to start at ToFu with detailed interest targeting. But as soon as you have 100 people in a custom audience (like 'Website Visitors'), you should launch a retargeting campaign. The key is to build from a solid, profitable base. Once your retargeting is working, you can confidently spend more at the top of the funnel to feed those warm and hot audiences.

Within each stage, you also need to test your ad creative. Don't just run one ad. Test at least 2-3 different images or videos and 2-3 different versions of your ad copy (headlines and primary text). Find a winning combination of creative and audience, then iterate on it. This methodical process removes the guesswork and is far more reliable than just "letting it run".

I've detailed my main recommendations for you below:

Pulling this all together, trial and error supported by ChatGPT isn't a strategy. It's gambling. To get consistent results from paid advertising, you need a systematic approach grounded in your business's real-world economics. The table below summarises the core action plan I'd suggest you adopt. It's a shift from focusing on vanity metrics and platform jargon to focusing on what actually drives profitable growth.

Following these steps will put you miles ahead of most people who are just boosting posts or following generic advice. It transforms you from a passive spender into an active, data-driven advertiser who is in control of their budget and their results.

Of course, this is a lot to take in and implement correctly. It requires a deep understanding of the ad platforms, constant monitoring, and the experience to interpret the data correctly. This is where professional help can make a huge difference. An expert can accelerate this entire process, helping you avoid costly mistakes and find profitable campaigns much faster than you could on your own.

We do this for our clients every day, building and managing profitable ad systems based on these very principles. If you'd like to have a chat and get a second pair of expert eyes on your specific situation, we offer a completely free, no-obligation initial consultation where we can review your strategy together.

Regards,

Team @ Lukas Holschuh