How to Measure Domain Attach Rate per Plan and Cohort

You sell hosting plans, but you also sell domains. Domains often carry higher margins than hosting, yet many resellers don't track how many customers attach a domain to each plan. Without that data, you can't see which plans drive domain revenue or how domain attach rate affects your overall contribution margin. This article shows you how to instrument and report domain attach rate per plan and cohort in your hosting billing system.

What is domain attach rate and why does it matter?

Domain attach rate is the percentage of hosting customers who also purchase a domain through you, either at signup or later. For example, if 100 customers buy a hosting plan and 30 also buy a domain from you, the attach rate is 30%.

Why does it matter? Domains typically have higher renewal margins and lower support costs than hosting. A 10% increase in attach rate can significantly boost your average revenue per user (ARPU) and contribution margin. But to measure that impact, you need to track attach rate per plan and per customer cohort—groups of customers who signed up in the same period or from the same campaign.

How to set up tracking in your billing system

Your billing system (like WHMCS, Clientexec, or Blesta) stores the data you need, but you must configure it to capture domain orders alongside hosting orders. Follow these steps:

• Enable domain registration and transfer products. Ensure your billing system has domain products set up with correct pricing and renewal dates.
• Link domains to hosting accounts. When a customer orders hosting, offer a domain registration step. Most billing systems allow you to create product bundles or add-ons. For example, in WHMCS you can create a product bundle that includes hosting and a domain. This links the two orders.
• Tag orders with plan and cohort identifiers. Use custom fields or order notes to record the hosting plan name and the signup cohort (e.g., month/year or campaign source). If your billing system supports it, use the API to add these tags automatically.
• Ensure renewals are tracked. Domains renew annually; hosting may renew monthly. Your system should record when a domain is attached and when it renews, so you can calculate lifetime value.

If you use a platform like Teculiar, which provides hosting automation and billing for resellers, you can define custom fields and use its API to tag orders programmatically.

How to calculate attach rate per plan and cohort

Once your data is tagged, you can query your billing system's database or export orders to a spreadsheet. Here's the formula:

Attach rate = (number of hosting orders with an attached domain) / (total number of hosting orders) × 100

Calculate this for each hosting plan and for each cohort. For example:

• Plan A: 50 orders, 15 with domains → 30% attach rate
• Plan B: 80 orders, 40 with domains → 50% attach rate
• Cohort Jan 2025: 100 orders, 35 with domains → 35% attach rate
• Cohort Feb 2025: 120 orders, 60 with domains → 50% attach rate

Use SQL queries or your billing system's reporting tools. If you're comfortable with code, write a script that pulls orders via the API and computes these metrics automatically.

How to measure contribution margin impact

Contribution margin is revenue minus variable costs. For domains, variable costs include registry fees and payment processing. For hosting, they include server costs, support, and control panel licenses.

To measure the impact of domain attach rate on contribution margin:

• Determine the contribution margin per domain. Subtract the registry fee and payment processing fee from the domain price. For example, if you sell a .com for $15 and the registry fee is $10, your margin is $5 (before payment fees).
• Determine the contribution margin per hosting plan. Subtract server costs, support allocation, and licenses from the hosting price.
• Calculate the blended margin per customer. For a given plan, multiply the attach rate by the domain margin and add the hosting margin. For example, if hosting margin is $10 and domain margin is $5, and attach rate is 30%, blended margin = $10 + (0.30 × $5) = $11.50.
• Compare across plans and cohorts. A plan with higher attach rate may have a higher blended margin, even if hosting margin is lower. This helps you decide which plans to promote.

Remember that domain renewals occur annually, so consider lifetime value over multiple years. A customer who attaches a domain may stay longer, increasing overall margin.

How to report and act on the data

Create a dashboard that shows attach rate and blended margin per plan and cohort. Update it monthly. Look for trends:

• Are newer cohorts attaching domains at a higher rate? If so, your checkout flow improvements are working.
• Which plans have low attach rates? Maybe the domain offer is not prominent, or the price is not competitive.
• Do higher attach rates correlate with lower churn? If so, you can justify investing in domain promotions.

Use these insights to adjust your marketing, pricing, and product bundles. For example, you might offer a free domain for the first year on a high-margin plan to boost attach rate.

What to do next

• Audit your billing system to ensure domain orders are linked to hosting plans and tagged with cohort data.
• Write a query or script to calculate attach rate per plan and cohort monthly.
• Compute contribution margin per domain and hosting plan, then blend them using attach rate.
• Set up a dashboard and review it with your team to make data-driven decisions.

To get started with a platform that supports custom fields and API access for this kind of tracking, see our pricing page.