Referring Domain Counting Rules: Subdomains and www

Two reports on the same website can show different referring domain totals, and the first instinct is to assume one of them is broken. More often the data is fine and the counting convention differs. Referring domain counting rules decide which part of an address becomes the unit, whether a subdomain, a www prefix or a country extension is merged or kept apart, and how repeat links are folded. This article walks through each rule, reports what Google documents about the Search Console Links report, and ends with a hypothetical convention you can adapt. If you are asking what are referring domains in the simplest sense: the number of distinct domains that link to a target. The word "distinct" is where your own rule has to draw the line.

Why Referring Domain Counting Rules Should Be Written Down

One site, three totals

Picture a hypothetical store owner who pulls three exports in the same week and gets three domain totals. One export counts every subdomain on its own, another merges them under the root domain, and the third only covers a recent crawl window. None of the three has to be wrong, because each answers a slightly different question. What went wrong is that nobody wrote the question down. For the basic idea of a link itself, what is a backlink covers the definition, so this article stays with the counting side.

Where an unwritten rule breaks comparison

If a monthly note says "domains went up", the reader cannot tell whether a new publisher appeared or an existing publisher opened a new subdomain. Without a stated rule, two months may not sit on the same scale. Writing the rule does not make the number bigger or more accurate. It only proves that this month and next month were measured with the same ruler, and that is what makes a drop or a jump discussable instead of mysterious.

Domain, Host and Root Domain Concepts

The layers of an address

Take a hypothetical address: blog.examplebrand.com/guides/page. Here "examplebrand.com" is the root domain, "blog.examplebrand.com" is a host (a subdomain of that root), and "/guides/page" is the path. Which layer becomes the counting unit is a rule you choose. With the root domain as the unit, links from a blog, a shop and a support subdomain collapse into one source. With the host as the unit, the same three links count as three sources.

What each unit answers

A root-domain unit leans toward the question "how many separate organisations linked to us?". A host unit leans toward "how many separate site sections linked to us?". Both are legitimate and neither replaces the other. That is why the first line of a written rule should name the unit in plain words, for example "Unit: root domain". Reports that mix units across months cannot be compared with each other.

Paths and parameters

The path never changes a domain total. A hundred links from a hundred pages of the same domain still equal one domain. Parameter variants and archive pages can make one link look like several rows, which matters more for link counts than for domain counts, but it still affects any raw export you group by hand.

Counting Subdomains Separately or Together

The case for merging

Merging subdomains under the root treats a brand's sections as one publisher. Three links from a news section, a blog and a forum of the same organisation become one source. If you are measuring variety, this prevents the same organisation from being counted repeatedly. How subdomains and subfolders differ on the site-architecture side is a separate topic, covered in subdomain vs subfolder decisions.

The case for separating

Separating makes sense when subdomains are run independently. On a hosting platform that hands every member a subdomain, each one may belong to a different person. Merging them would turn many unrelated owners into a single source. Asking who controls the subdomain is therefore the question that decides which rule fits.

A mixed rule with an exception list

Many teams merge by default and keep a short exception list with a reason beside each entry. If the list grows long, the rule becomes hard to read, and switching the unit to host may be the cleaner choice.

www and Non-www Versions

Two addresses for one site

Technically www is a subdomain, but on most sites it behaves like an alias for the same content. A publisher may link to the www version once and to the bare version another time. With a root-domain unit those two links come from one source. With a host unit they may show up as two rows, and the same publisher is counted twice. To settle which version your own site should present, www vs non-www standardization is the natural companion read.

The same problem on the target side

The confusion is not limited to sources. If some links point to your bare address and others to the www address, and redirects are not consistent, a target-level export will list two targets. Note in the same line of your rule which address you normalise to.

Old addresses and redirect chains

A site that moved between versions may still receive links aimed at the earlier address. The redirect carries visitors correctly, yet the target-level table keeps old addresses as separate rows. Keep a mapping column in your export so those rows can be grouped under the current address.

Country Extensions and Brands With Several Extensions

Do extensions merge?

Google's Search Console help page for the Links report says top-level domains are not omitted when grouped, so a .com address and a country-extension counterpart show up as separate sites. That is the behaviour of that report, not a requirement for your own rule. If a brand runs .com, .com.tr and .de versions, you decide whether it counts as one publisher or three domains.

A brand with two languages

Imagine a hypothetical brand with examplebrand.com and examplebrand.com.tr, written in different languages. A link from one and a link from the other may reach two different audiences. If you measure variety, count them apart. If you are removing same-owner duplicates, merge them. The wider planning question for multilingual outreach is in international multilingual backlink strategy.

Second-level extensions

Some countries use two-part endings such as .com.tr or .co.uk. A script that splits at the last dot will treat every such site as one giant domain. If you group by hand, use a list of known two-part endings and check twenty random rows after the first export.

Platform Subdomains and Shared Hosting

Member subdomains

Blog platforms and site builders often give each member a subdomain under the platform's domain. A hypothetical address like memberblog.platform-example.com may be one of hundreds, each owned by a different person. A root-domain rule turns them all into one domain, while a host rule counts each separately. Which is more faithful depends on how much you care about who the linking author is.

Shared servers and corporate networks

Independent sites on the same server count as separate domains as long as their domain names differ; a shared server or IP is not a counting unit. A company that runs ten domains as a blog network yields ten domains under a root-domain rule. When you notice this, attach a "same owner" note to those rows rather than changing the rule, and only label ownership you can actually confirm.

Sampling a platform-heavy list

When a large share of your rows belong to one platform domain, review a handful of those rows by hand before deciding the rule. Open the linking pages, see whether the authors differ, and write down what you found. A rule built on a sample you actually read is easier to defend than one inherited from a default setting.

The Grouping Logic of the Search Console Links Report

What the help page says

According to Google's Search Console help page, the Links report groups data by root domain. Subdomains and subdirectories are merged in that grouping, and top-level domains are not. Duplicate links from the same source to the same target are consolidated. Tables are limited to 1,000 rows, and the report is a sample meant to show your overall link profile, not a comprehensive list. It also does not say whether a link is nofollow.

What it does not say

That page does not describe a metric called "referring domains", and it does not say Google weighs such a number in ranking. The sites-that-link figure is a view shaped by the report's own grouping. Place it next to a third-party tool's figure only after remembering that the two rules may differ. For reading a profile end to end, reading a backlink profile with link checkers is a useful starting point.

Reading the row cap

Because tables stop at 1,000 rows, a heavily linked site cannot read the hidden remainder from the screen. Describe the figure as "within the report sample" instead of presenting it as a total.

Mapping a Tool's Counting Logic to Your Own Rule

Three questions for the tool documentation

Each tool counts in its own way, and nothing here asserts how any named product counts. Read your tool's documentation for three things: whether the unit is root domain or host, whether country extensions are merged, and how repeated links are handled. If the documentation is silent, a written question to the vendor beats guessing. Treat every tool total as that tool's own output, never as a number Google reports.

The mapping table

Write the answers in a two-column table, your rule on the left and the tool's behaviour on the right. Where they differ, add a third column with the step that closes the gap, such as regrouping the export by root domain by hand. Build it once and reuse it until the tool or the rule changes. The same caution holds for authority scores, which domain authority vs domain rating explains for two well-known names of that kind of score.

Putting two tools side by side

When two tools disagree, align the units before chasing the gap. Convert both lists to the same unit, then check repeat-link handling and crawl windows. If a difference remains, it is a data-coverage difference between the tools. Pick one as the primary source rather than averaging the two.

Adding the Counting Convention to Reports

One paragraph per report

The convention does not need to be a long document. A footnote with the tool, the export date, the counting unit and the exceptions is enough. Whoever reads the number should find how it was counted on the same page. For the rest of the report layout, the monthly structure in building a monthly SEO report can hold the footnote.

A number needs a date and a scope

A domain total alone says very little. Write "212 domains (hypothetical figure, root-domain unit, month-end export)" and the number stops drifting into other meanings later. In reports for clients or managers, that suffix closes most objections before they are raised.

Explaining it in two sentences

In a meeting, two sentences are enough: the unit you count, and why other reports may show a different total. A line such as "subdomains are merged under the root domain, so another tool may show a higher figure" answers most questions in advance. Talk about the rule, not the number, when confusion appears.

Recalculating Old Data When the Rule Changes

What triggers a change

Three situations justify a rule change: switching tools, changing site structure such as moving to a subdomain, or a reader asking a different question. Every change goes in a written log with an effective date. Changing a rule silently creates a spike on the trend chart that never happened in the real world.

Recompute or annotate

If old exports can be regrouped under the new unit, recompute earlier months and keep both series side by side. If not, add a note on the chart marking the change date and do not join the two periods with a line. Do not delete the old series, because it remains your evidence when someone asks why.

Version numbers and the change log

Give each rule a version and record the date, the reason and the approver in one log. A hypothetical entry might read "Version 2: subdomains merged, platform subdomains moved to the exception list". Even three lines of log explain a discontinuity six months later.

Example Template: A Referring Domain Counting Convention (Hypothetical)

The table and every domain name below are hypothetical. They are not a real site, tool or client record. Fill it in with your own rules.

To prepare the convention, work in this order:

1. State in one sentence what question the report answers.
2. Pick the counting unit and give a one-line reason.
3. Decide www, subdomains and country extensions separately.
4. List exceptions such as platform subdomains in a short list.
5. Compare against your tool's documentation and note the differences.
6. Add the effective date and who approved the rule.

The report footnote can carry these items:

• The tool name and the export date.
• The counting unit and the exception list.
• One sentence saying the figure belongs to that tool.
• The change date, if the rule has changed.

Frequently Asked Questions

How are referring domains counted?

A referring domain total is the number of distinct domains that link to a target at least once, so fifty links from one domain still count as one source. Which address layer is the unit depends on the tool and on your rule. Always publish the number together with the rule, tool and date.

Do subdomains count as separate domains?

It depends on your convention. With the root domain as the unit, blog.example.com and example.com are one domain; with the host as the unit they are two. The Search Console Links report merges subdomains under the root domain, but that is the report's behaviour and not every tool does the same.

Are the www and non-www versions the same domain?

Under a root-domain unit they merge into one source. Under a host unit the two forms can produce two rows. Choose one approach, write it in the report footnote and apply the same choice every month, since consistency matters more than which option you pick.

Are country extensions counted as different domains?

The Search Console Links report does not merge top-level domains, so country-extension versions appear separately there. In your own convention it is a choice. Count them apart if you want to read different markets as different audiences, and merge them if the goal is to remove same-owner duplicates.

Why do tools count differently?

Tools can differ in crawl data, repeat-link handling and domain-merging logic, so one tool's total rarely matches another's. Each total belongs to the tool that produced it and is not a Google value. Read each tool's documentation for its rule, and compare figures only after aligning the units.

Who should approve the counting convention?

The person who prepares the report drafts it, and the person who uses the numbers to decide, such as the client or team lead, approves it. The approval shows both sides read the same figure with the same meaning. Record the approval date and approver, and renew it whenever the rule changes.

Conclusion and Next Step

A referring domain total is a summary produced by one choice of address layer, and it misleads when that choice stays unwritten. Start with the unit, settle www, subdomains and country extensions, then carry the whole thing into your report footnote. The convention is not a Google measure and it does not move rankings; it only keeps month-to-month comparison honest.

When you are ready to acquire links, fix the target page and the placement you want first, and then read the products on the backlink packages page against your convention. On Akua the order runs through the cart and payment, then the seller reviews and approves, a delivery notice follows, and a dispute is available if the delivery does not match the order. Recording the delivered domains under your own counting rule remains your task.