Ask buyers how long their CMS migration took and few can give a clean start-to-finish number: the project ran in phases, started before they joined, or is still going. What they describe instead is where the time goes. Content and templates must be assessed, transferred, transformed or rebuilt; companies with many sites often migrate in waves; and features the old platform provided may need to be recreated. Delays also arise before implementation, when budgets change, priorities shift or the platform and agency decisions remain unresolved. None of the projects where buyers compared the schedule with a plan was reported on schedule — the same pattern buyers describe for email, commerce and loyalty platforms — and more of those slips were pauses than overruns. The companion reads are why companies switch CMS platforms, which covers what happens after the move, and what headless CMS buyers wish they'd known, where the ratings live.
Why CMS migrations take longer than planned
Content and templates take more work than expected
The content workload is the source of effort buyers describe most. Depending on the old and new architectures, teams may need to rebuild templates, transform content models, move pages and archives, or rewrite material that cannot be carried across directly; some content moves in batches, while other material needs manual attention. Buyers with large sites and deep archives describe this work extending the project substantially. One B2B distributor calls its move “a very labor-intensive lift in rewrite of all of our pages that are moving to Optimizely.” At a global electronics company, “the last, I would say probably year, year and a half has been the migration of content over to this.” A consumer brand on a long migration sees no quick end: “We are slowly migrating, but I don't see that another two or three years down the line we'll be migrated fully,” because “there are lots of pages, there's not one page or two page.” Publishers carry archives: “we need to bring on legacy articles and content from the 70s all the way until modern day”. What a rebuild involves is on the Contentful stack.
Named in this context: Optimizely · Contentful · Adobe Experience Manager
Many sites become waves, and waves become years
Companies with many brands, divisions or markets cannot move everything at once, so they move in waves and the program runs for years. One company “picked certain divisions within the company to be the ones that are launching first and then, because it's just we can't do it all at once.” A home-products manufacturer rebuilding its sites says “we've got a lot of sites, so it'll be a while.” At one global company, “It's been three years and that AEM site is on-prem,” with the larger regional sites still to come “in at least couple of years because they're big.” Commerce replatforms roll out market by market in the same way; those are on ecommerce replatforming timelines.
Named in this context: Adobe Experience Manager · Contentful · headless platforms
What the old platform did has to be rebuilt
Personalization, testing and recommendations that the old suite handled have to be rebuilt or relearned on the new one, and that work lands on the schedule. A financial services company moving off a suite expected to “learn the intricacies of doing things like personalization, things that we could do in Sitecore, because we've been using that system for years.” How long it takes to get back to where the old site was, after launch, is covered on why companies switch CMS platforms.
Named in this context: Sitecore · Adobe Experience Manager
Budgets and priorities pause the project
The most common shape of slip here is not a build that ran long but a project stopped before or during the build. A healthcare distributor says “We were supposed to migrate four websites on Sitecore this year, but it got pushed due to budget constraints, and we don't know when” — “So we're in a waiting pattern at the moment.” A food retailer had hoped to move that year, “but as of probably about a week or two ago, I was told to put all developments on pause while budgets were being reevaluated”. Elsewhere a migration “got delayed a little bit because of some internal changes that happened,” and only later “is starting to be reignited, let's say, and taken off pause”.
Named in this context: Sitecore · Liferay · Adobe Experience Manager
Platform and agency decisions delay the start
Some companies spend months or years evaluating a replacement before implementation begins. That extends the overall modernization program, though the selection period is distinct from the migration's build and cutover. One media company's editors complained for years before an RFP was run; another company hired an agency to choose its platform after months of evaluation; a hotel group's replatform moved from one year to the next while it changed agencies and reran its selection. As with loyalty programs, the clock starts long before the build.
Named in this context: Sitecore · Kentico · agencies
New hands: a new agency or a new architecture
A change of who builds the site, or how, sets the pace. A hotel group waiting on its new agency put it this way: “We're still on Sitecore, but when the new agency starts, I believe we're moving to a new platform, but I'm not sure what that is 100% yet.” Two buyers say a team new to headless delivery slowed them; one says the move to a headless architecture “has really impacted our ability to deliver quickly at scale”. What headless changes for a team is on what is a headless CMS.
Named in this context: Sitecore · headless platforms · agencies
How long does a CMS migration take?
These interviews do not establish a typical duration: few buyers give a full start-to-launch time, and the ones who do describe different projects. Among the single-site moves that finished, buyers describe anywhere from three or four months — a lift and shift that carried old problems forward — to well over a year for a full rewrite or a version change. The one multi-market program that finished took about a year for its home market and about another year for the rest. Every global or multi-brand program that gave an elapsed time was still running, after one to more than three years. Single-site moves sit in about the same range as moving a single-brand online store, which is on ecommerce replatforming timelines. Read the figures as examples, not benchmarks.
Is a CMS upgrade easier than switching?
Not necessarily. Version changes inside the same vendor run as migration-sized projects in these interviews, because the site has to be rebuilt for the new version: a move from one generation of Sitecore to its headless version, planned at six months, took about fifteen months to the interview and about eighteen to finish, and a Kentico version upgrade took about a year of dedicated staff time to move the content. A third buyer says a Sitecore update that skips several years of versions can take many months. The switching page notes that an end of support tends to keep companies with the same vendor; staying is not always the cheap option it looks.
Do CMS migrations stay on schedule?
Not in the cases with usable timing comparisons here. Seven projects have both an identifiable original plan and a reported outcome or later schedule status, and none was reported to be on schedule — the same pattern buyers describe for email, commerce and loyalty platforms. Three finished or launched later than planned: one rebuild took about twice its plan, the version change above took about three times its plan, and a new website launched six or seven months after the date the team had expected. The other four were paused or pushed back before or during implementation — twice for budget, once for internal changes, and once while the company changed agencies and reran its selection — and had not necessarily finished by the interview. This small, selectively reported group cannot establish how often CMS migrations miss their dates overall. A slip has knock-on costs: one team bought a testing tool for its new site and could not use it until the site launched.
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The counter-current: the moves that went quickly
The quick or smooth moves here share a shape. A lift and shift, with the site moved largely as it was, finished in “three months, or three to four months” — with the old site's problems carried across, as the switching page records. Phasing by content type inside a group went well: one brand has been “migrating onto Amplience throughout this year, just kind of content bucket by content bucket,” a move a later interview confirmed was complete, and finds “It's a whole lot less buggy than AEM was.” A pilot can de-risk a global program — “We had run a pilot for six months, and that was a very successful pilot.” And small sites can now take weeks: one manufacturer has “developed two to three new websites in a matter of weeks versus going out to a developer and taking months.” Nothing quick here involved rewriting every page onto a new architecture.
What this means for your migration plan
In these interviews the length of a CMS migration is set by the content that has to move, the number of sites, and whether the project keeps its budget and its team, more than by the platform. Our recommendations, not practices buyers describe: count the pages, templates and archives and decide what moves in batches, what needs rewriting and what can be left behind before setting a date, since content is where buyers say the time goes; decide which features of the old platform — personalization, testing, recommendations — must work on day one and plan their rebuild as its own track; if you have many sites, plan the waves and the period of running two platforms, and pilot the first wave before committing the rest; secure the budget for the whole program, since pauses caused more of the slips here than overruns; and treat a major version upgrade as a migration, with the same planning. For what to expect after launch, see why companies switch CMS platforms.
Common questions
How long does a CMS migration take?
These interviews do not establish a typical duration. Among single-site moves that finished, buyers describe anywhere from three or four months — a lift and shift that carried old problems forward — to well over a year for a full rewrite or a version change. Multi-brand and global programs run for years, a few brands or content types at a time, and most of the ones here are still running.
Why do CMS migrations take longer than planned?
Buyers most often describe the work of moving, transforming or rewriting content and templates, many sites turning into waves of migration, features the old platform had having to be rebuilt or relearned, budgets and priorities pausing the project, and platform and agency decisions that delay the start. Among projects where buyers compared the schedule with a plan, none was reported on schedule — some finished late, and more were paused or pushed before finishing — though this small group cannot show how often migrations miss their dates overall.
Is a CMS upgrade easier than switching platforms?
Not necessarily. Buyers describe version changes inside the same vendor that took about a year or longer, one of them planned at six months, because the site had to be rewritten for the new version. An upgrade can be a migration-sized project.
Should you migrate all your websites at once?
Buyers with many sites in these interviews move a few brands, divisions or content types at a time and review the results between waves, and the phased moves here are among the ones that went smoothly. Phasing also stretches the program over years, so the old and new platforms run side by side for a long time.
Does moving to a headless CMS slow the migration?
Two buyers in these interviews say a team new to headless delivery set the pace, along with rewriting every page. Most of the timed projects here moved to headless platforms, so there are too few others to compare, and these interviews do not show whether headless moves take longer.
How long does a CMS migration take compared with an ecommerce replatform?
In these interviews, single-site CMS moves that finished took about as long as moving a single-brand online store, from a few months to about a year, and both run for years when many brands or markets move in waves. Neither category establishes a typical duration from the examples buyers give.
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