The question has a bad reputation because it is usually answered badly. Ask most agencies how many backlinks you need and you will get a shrug dressed up as sophistication: it depends. It does depend. It depends on four things, all of which are measurable in about ten minutes, and at the end of those ten minutes you have a number rather than a posture.
Here is the arithmetic, the two places it goes wrong, and what the answer typically looks like in B2B SaaS.
The subtraction that produces the number
Pick the single page you actually need to move. Not your domain, not your blog — one URL with a commercial job. Then open the search result you want to win and take the four URLs currently above it.
For each of those five URLs, count referring domains at page level. Not domain rating. Not total backlinks. The number of distinct domains linking to that specific URL. Any backlink tool will give you this in one screen; the free tiers are sufficient for five URLs.
There are two ways to finish the sum, and they answer slightly different questions.
The median. Take the middle of the four and subtract yours. If the pages above you carry 84, 71, 96 and 63 referring domains and you carry 19, the median is roughly 78 and your gap is 59. This is the number to plan a budget against: it is what a typical competitor has, not what the strongest one has.
The pooled remainder. Combine all four lists, de-duplicate, then remove every domain that already links to you. In the same example that leaves 88 domains. This is the stricter figure and it is the one to build a target list from, because every domain in it is a publication that demonstrably covers the category and does not yet cover you.
Use the median for the plan and the pooled remainder for the outreach list. Either way you now have a real number. It tells you the volume, it tells you the budget when you multiply by a credible per-placement cost, and it tells you the timeline when you divide by a sustainable monthly rate. None of that is available from it depends.
Why page level and not domain level
This is the single most common way the calculation goes wrong, and it goes wrong in both directions.
Compare at domain level and a large competitor looks unreachable. A company with 4,000 referring domains across its whole site looks like a fortress. But the page outranking you may carry eleven of them. You are not fighting the company. You are fighting one URL, and that URL is often surprisingly thin.
The reverse error is more expensive. A small competitor with 300 domains site-wide can have a category page carrying 90 — because they built it deliberately and pointed everything at it. At domain level they look beatable. At page level they are three years of work ahead of you.
We have declined engagements on the strength of this one check. A company came to us convinced they faced a two-hundred-domain deficit because that is what the domain comparison showed. At page level the gap was six. They did not need a link building agency; they needed to fix an internal linking problem and wait a quarter.
The four things the number actually depends on
The subtraction gives you a first figure. Four factors move it, and knowing which one is biting matters more than the precision of the estimate.
Query commercial intent. A comparison page for a category term needs materially more than an informational page in the same category. Commercial SERPs are where everyone is spending, so the equilibrium sits higher. If your target is a "best X software" term, expect the gap you measured to be the floor rather than the middle.
How contested the category is right now. Your competitors are not standing still. If the four above you are each acquiring five domains a month, you are not closing a 42-domain gap — you are closing 42 plus whatever they add while you work. Check their referring-domain growth over the last six months before you commit to a timeline. This is the factor most plans quietly ignore.
Whether the page can hold the position. Links move a page up. They do not keep it there. If your target page answers a different question than the query, or lacks the comparison table and pricing honesty that all four competitors have, authority will lift it and the click-through will push it back down. We treat this as a hard gate: no acquisition begins until the page reads like it deserves the position.
What your existing profile looks like. Nineteen referring domains earned over four years from genuine trade publications is a different starting point from nineteen bought last quarter from a network. The second case needs remediation before addition, and remediation is not a link building problem.
What the number usually is in B2B SaaS
Across the audits we have run, the page-level gap in B2B SaaS categories lands between fifteen and ninety far more often than outside it. That range is worth internalising because it contradicts the two loudest voices in the market.
It contradicts the agencies selling volume, because ninety domains at a sustainable eight a month is under a year — not a permanent retainer. And it contradicts the founders who assume the category is unwinnable, because fifteen is a quarter's work.
The distribution matters more than the average. Vertical SaaS categories — software for veterinary practices, for freight brokers, for clinical trials — routinely show gaps under twenty-five, because the whole category has fewer than a hundred credible publications and nobody has done the work. Horizontal categories where every marketing team in the world is competing show gaps past ninety and competitors still acquiring.
If you are in the first group, the honest advice is usually that you need less than you think and should start now. If you are in the second, the honest advice is that you need a bigger commitment than the budget implies, and the failure mode is starting anyway.
Turning the number into a plan
Once you have the gap, three divisions turn it into something a board can approve.
Months = gap ÷ sustainable monthly acquisition. Sustainable is the operative word: a rate you can hold for the whole period, not the rate of your best month. In B2B SaaS a well-run programme places four to twelve a month depending on category size.
Budget = months × monthly rate. Credible B2B SaaS placements run roughly $150 to $500 each across the market. If the implied per-placement cost of a proposal sits far below that band, the inventory is coming from somewhere that will not survive scrutiny.
Commercial effect = months + sales cycle. This is the one people forget. A link earned in month nine does not become revenue in month ten if your sales cycle is nine months. Add the cycle to the acquisition timeline before you promise anyone a payback date.
If that final number lands past twenty months, the arithmetic has told you something important: at this budget, against this gap, buying links is the wrong instrument. Either narrow the target to a page with a smaller gap, raise the sustained monthly figure, or spend the money on the product and the page instead. We say this in about a third of the audits we run, and it is the most useful thing in the document.
The check that takes ten minutes
You do not need us to do this. Open your target page, open the four URLs above it, pull page-level referring domains for all five, take the median of the four and subtract your own. Then check whether those four are still acquiring, and read your own page honestly against theirs.
Ten minutes gets you a number, a direction and a rough timeline. What an audit adds is the reachable publication list — whether the domains you need actually exist and will take you — and that is a genuinely harder problem. But the number itself is yours for the cost of an afternoon, and having it before you take a sales call changes the conversation entirely.