A business that made 800 sales on 200,000 TL of ad spend last month may have made 880 sales on 250,000 TL this month. Sales grew 10% while the budget grew 25%. In this case, the cost per sale goes up. But before cutting spend, you need to look at the change in revenue and see which campaigns drove this result.
When comparing ad performance across Google Ads and Meta Ads, percentage changes are only the starting point. To understand how campaigns performed against last month, budget, conversion and revenue data should be reviewed together, and then the source of the change should be investigated.
How Do You Compare Ad Performance Month Over Month?
A difference between two months' data does not always come from a change in campaign performance. The number of days in each month, the promotion calendar or a change in conversion tracking can all affect results. That is why the scope of the compared periods should be defined before you start the report.
How Should You Choose the Date Range to Compare?
When comparing the total results of completed months, you should also look at daily averages. Because October has 31 days and September has 30, part of the difference in total spend and conversions may come simply from the number of days.
In Google Ads, you can compare against the previous period or the same period last year using the date range selector. In Meta Ads, you can likewise review spend, conversions and cost results side by side across the same date ranges.
Before reporting, check the following variables:
Are the same conversion actions being measured in the campaigns?
Have attribution or conversion value settings changed?
Have there been changes to budgets, bidding strategies or campaign goals?
Are product prices, stock levels or discount conditions different?
Is there a seasonality effect in the compared periods?
An equal number of days does not always mean similar conditions. The split between weekdays and weekends or the campaign calendar may differ. Especially in periods like the November sales, the same period last year and budget targets should be used as references alongside the previous month.
Conversion Delay and Measurement Changes
Users who click an ad do not always complete a purchase or submit a form on the same day. In Google Ads' standard conversion columns, conversions are generally attributed to the date of the ad interaction. If a user buys a few days later, the conversion count for that past date can change.
For this reason, the CPA and ROAS values of a recently completed month can be updated in the following days. Conversion delay should be taken into account, especially when making budget decisions based on the last days of the month.
If changes have been made to the measurement setup, this should be noted in the report. If only purchases were counted last month but add-to-cart actions are included in primary conversions this month, comparing the two periods' results becomes harder.
How Should You Interpret Changes in Spend, Conversions, CPA and ROAS?
As a campaign's budget increases, its sales may not grow at the same rate. In such a case, the first thing to check is how the spend increase translated into conversion volume and revenue.
| Metric | What to Check When It Changes |
|---|---|
| Ad spend | In which campaigns did the budget increase occur? |
| Number of conversions | Did sales or leads grow at the same rate as spend? |
| Ad revenue | Is the revenue increase tied to the number of sales or to order value? |
| CPA | Do CPC or conversion rate play a part in the cost increase? |
| ROAS | Is the change driven by CPA or by average conversion value? |
| MER | How does total sales revenue move relative to ad spend? |
Percentage change is calculated with this formula:
Percentage Change = ((This Month's Value - Last Month's Value) / Last Month's Value) × 100
If the previous period's value is zero, the absolute difference should be used instead of percentage change.
How Did the Budget Increase Translate into Sales?
If spend grows 30% while conversions grow 10%, the cost per sale has risen. However, selling products with a higher basket value can affect revenue performance in a different direction.
Looking only at the percentage change is not enough here either. A small campaign that drops from five sales to three has a different impact on the business than a high-budget campaign that falls from 500 sales to 300. In your analysis, absolute change, data volume and spend size should be considered together.
How Should You Read the Change Between CPA and ROAS?
If cost per purchase rises while average order value grows at a higher rate, ROAS may increase. Conversely, if sales are achieved at a lower cost but order values shrink, ad revenue and ROAS may fall.
Knowing how ROAS is calculated is the first step in interpreting these changes. In a monthly comparison, the focus should be on which campaign or product group is behind the movement in the metric.
In lead-focused campaigns, lead quality should be interpreted together with cost. Suppose last month 100 forms were collected at a cost of 250 TL each and 30 of them were qualified, while this month 100 forms were collected at a cost of 200 TL each and only 15 were qualified. The cost per form has dropped. Even so, the cost per qualified lead has risen from about 833 TL to 1,333 TL.
How Do You Find the Cause of a Performance Change?
If the cost per click was 12 TL last month and has risen to 16 TL this month, the same budget buys less traffic. If CPC is stable but sales are declining, it makes more sense to look at the change in conversion rate before looking at ad costs.
Examining Ad Costs with CPC, CPM and CTR
If you are getting less traffic for the same budget, you can check the changes in CPC and CPM. If CPM rises while CTR stays flat, you would expect the cost per click within the same measurement scope to rise as well.
If CTR falls while CPM stays at a similar level, you can review ad creatives, messaging and audience distribution. Since differences in placements or impression distribution can also affect click-through rate, it would not be appropriate to attribute the change solely to creative performance.
If CTR rises in the monthly report but conversions decline, you should investigate whether the clicks are turning into sales. If users have low purchase intent, driving more traffic may not improve conversion performance.
Examining Site Performance with Conversion Rate and Order Value
If CPC stays largely stable while CPA rises, conversion rate may have dropped. At this stage, landing pages, product stock levels, price changes and the checkout process should be checked.
The conversion rate in Google Ads and the session- or user-based key event rate selected in GA4 may not be based on the same measurement logic. In a monthly comparison, the same data source and the same conversion definition should be used.
If ROAS falls while the number of sales stays flat, average order value should also be examined. An increase in the share of lower-priced products in sales can reduce ad revenue without changing the number of conversions.
Monthly Ad Performance Comparison Example
In the fictional e-commerce scenario below, ad spend increases 33.3% while revenue attributed to ads grows 20%.
| Metric | Last Month | This Month | Change |
|---|---|---|---|
| Ad spend | 300,000 TL | 400,000 TL | +33.3% |
| Ad revenue | 1,500,000 TL | 1,800,000 TL | +20% |
| Number of sales | 1,200 | 1,500 | +25% |
| CPA | 250 TL | 266.67 TL | +6.7% |
| ROAS | 5.0 | 4.5 | -10% |
| Average order value | 1,250 TL | 1,200 TL | -4% |
In the period when 100,000 TL more was spent on ads, reported revenue increased by 300,000 TL. The ratio of the revenue difference to the spend difference is 3.0. However, not all of this difference may have come from the additional ad budget. Discounts, organic traffic and shifts in brand demand may also have affected sales.
The fact that sales grew 25% while average order value fell 4% shows that revenue growth lagged behind the increase in the number of sales. You should investigate which product groups the spend increase occurred in and whether the share of low-value orders has risen.
In this table, instead of simply cutting the budget, you should look at results at the campaign level. Campaigns whose spend is rising while conversions stay flat should be separated from those that are increasing sales within the target cost range.
Products' contribution margins should also be factored into the budget decision. An increase in revenue does not mean the business is earning proportionally more profit.
How Can You Analyze Monthly Ad Performance with AdsLuma?
When preparing a monthly report, you may need to review the change in spend in Google Ads, conversions in Meta Ads and traffic results in GA4 separately. In AdsLuma, this data is tracked on a shared dashboard, so changes across channels can be evaluated in one place.
In the earlier example, ad spend rose 33.3% while ROAS fell 10%. On AdsLuma's ad performance analysis screen, you can examine which campaigns used more budget and how conversions changed. By including organic traffic results in the analysis, you can look at the change in sales performance within a broader frame.
You can ask the Luma AI marketing assistant questions like these based on your campaign data:
“In which campaigns did spend rise while conversions declined compared to last month?”
“Evaluate the changes in Google Ads and Meta Ads performance together and give budget recommendations.”
Luma AI can interpret performance changes based on the data it has access to and help identify the campaigns that need investigation. The scope of its assessments varies depending on the connected data sources and the available reporting data. AdsLuma's automated monitoring and alert features can also be used to track changes such as inefficient spend, conversion drops or traffic loss.
Turning the Monthly Performance Comparison into a Budget Decision
Once the monthly analysis is complete, campaigns can be divided into three groups based on their results: those whose budgets can be increased, those that need optimization and those to keep monitoring. For campaigns that are growing at the target CPA and ROAS level, a budget increase can be considered. For campaigns whose spend is rising while sales volume declines, traffic cost, conversion rate and targeting changes should be investigated.
For each campaign, the action to take, the KPI to track and a re-evaluation date should be set. Next month's report should also be used to see how these decisions affected performance.
Frequently Asked Questions About Monthly Ad Performance Analysis
Which metrics should you look at first when comparing ad performance with last month?
Spend, number of conversions, ad revenue, CPA and ROAS are the first metrics to compare. They show how budget usage translated into sales or lead results. CPC, CPM, CTR and conversion rate can then be used to investigate the causes of the change. Alongside percentage changes, absolute differences and data volume should also be taken into account.
How is percentage change calculated in monthly ad performance?
Subtract last month's value from this month's value. Divide the result by last month's value and multiply by 100. For example, ad spend that rises from 100,000 TL to 125,000 TL has increased by 25%. If the previous period's value is zero, the absolute difference should be shown instead of percentage change.
Why might conversions fall even though ad spend has increased?
A rise in CPC or CPM, a decline in conversion rate, audience changes, stock issues and landing page performance can all cause this. First compare traffic costs and conversion rate, then investigate which campaigns the change is concentrated in. Measurement issues and conversion delay should also be checked.
Should you look at the same month last year in a monthly ad performance comparison?
In industries where seasonality is strong, it is useful to examine the same period last year. The previous month shows short-term change, while a year-over-year comparison helps you understand the seasonal effect. However, if budgets, product range or measurement conditions have changed, these differences should be factored into how you interpret the results.
Can Google Ads and Meta Ads results be compared in the same report?
The two platforms' spend, impression, click and conversion data can be reviewed in a shared report. However, because their attribution methods can differ, the reported conversion and revenue values should not be added together directly. While channel-level performance is evaluated separately, total sales results should be checked against the order system or a suitable central data source.
