The optimal approach for a site of this scale is a staged, section-by-section migration built on a complete pre-migration audit and 1:1 URL mapping, not a single flash-cut of all 500,000+ pages at once. Google’s own site-move documentation explicitly recommends that large sites move a portion of the site first to observe effects on traffic and indexing, then proceed with the rest in chunks or all at once once that initial phase is validated, precisely because a full simultaneous cutover on a site this size makes it far harder to isolate the cause of any problem that appears, and forces Google to reprocess an enormous number of URLs in the same crawl window. At this scale, the trough is not primarily a redirect-correctness problem, it is a crawl-capacity and reprocessing-capacity problem: Google has to recrawl every migrated URL, evaluate the redirect, transfer signals, and re-render each page, and that work is bounded by how much of your site Google is willing and able to crawl in a given period. No published Google guidance ties trough duration or depth to page count, so any specific number of weeks or percentage of traffic dip promised for “a 500K+ page site” is not something Google has stated and should be treated as fabricated if you see it cited as fact.
Why crawl budget, not redirect logic, is the real constraint at this scale
A correct redirect map (accurate, permanent 3xx status codes, one old URL mapped to one true new equivalent, no redirect chains or loops) is necessary but not sufficient to control the trough. The actual bottleneck at 500K+ pages is how quickly Google’s crawling infrastructure can revisit every old URL, confirm the redirect, and transfer the ranking signals to the new URL, and Google does not crawl unlimited volume instantly on your schedule. Crawl demand and crawl capacity are finite and are themselves influenced by the perceived value and freshness needs of your site, meaning a simultaneous cutover of hundreds of thousands of URLs creates a backlog: URLs sit in a “redirect seen, not yet fully processed” state for longer simply because there are more of them competing for the same crawl allocation, extending the period during which some portion of the site is in transitional limbo in the index.
Staging the migration by site section (a product vertical, a content hub, a subdirectory) rather than committing the entire domain at once directly addresses this constraint in two ways. First, it keeps each individual batch within a volume Google can process in a reasonable window, rather than asking Google to reprocess your entire index footprint simultaneously. Second, and just as important operationally, it isolates failure. If a redirect logic bug, a canonical conflict, or a template regression is only discovered after go-live, a staged rollout confines the blast radius to the section that moved, leaving the rest of the site’s rankings and crawl relationship with the old domain untouched while you fix the issue. A single big-bang cutover that goes wrong puts the entire 500K+ page footprint at risk simultaneously, with no unaffected control group left to compare against.
A hypothetical illustration of staging containing a failure
Hypothetically, imagine a large enterprise retailer, “Corcoran & Vale,” migrating a 600,000-page catalog to a new domain, choosing to move its lower-traffic “discontinued items” section first as the initial phase before touching the flagship product categories. Shortly after that first phase goes live, monitoring reveals the new template’s canonical tag generation breaks for a specific edge case, products with no listed subcategory, causing those pages to self-canonicalize incorrectly. Because only the discontinued-items section had moved, the bug’s effect is confined to a comparatively small, lower-value slice of the catalog while it gets diagnosed and fixed. Had the same bug shipped as part of a single full-site cutover, it would plausibly have affected the same edge case across the entire 600,000-page catalog simultaneously, including the highest-traffic categories, before anyone had a chance to catch it.
The practical phase-by-phase approach
Pre-migration audit and pruning. Before building any redirect map, audit the existing 500K+ page inventory rather than assuming every page must be preserved. At this scale it is common for a meaningful share of pages to be orphaned, duplicate, thin, or effectively dead weight that has accumulated over years. Migrating dead weight 1:1 just carries the same crawl burden and potential quality signal problems onto the new domain. Decide deliberately which pages get a real redirect to a true equivalent, which get consolidated (many old URLs redirecting to one strong new hub page, only where that’s a genuine content match), and which are deliberately let go (410 or left to 404 naturally) because they never should have been indexed in the first place.
Full 1:1 URL mapping for everything that survives. Every URL that is kept needs a specific, accurate mapping to its new-domain equivalent, not a generic pattern-based redirect to a category page or homepage. Redirecting mismatched content (old specific page to a generic new landing page) is one of the most common causes of a deeper and longer trough than the migration itself required, because it signals a poor content match and can cause Google to treat the redirect target as a weaker equivalent rather than a true continuation.
Staged rollout by section, not a single flash cut. Move one bounded section first, a single template type, a single subdirectory, or a single content vertical, and hold the rest of the site in place on the old domain while that first phase is monitored. Choose a first phase that is representative but not your highest-value traffic driver, so you have a meaningful test without exposing your most critical revenue-generating pages to first-mover risk. Only proceed to the next phase once the first phase shows expected indexing and ranking behavior on the new domain.
Long-term redirect maintenance, not a short window. Redirects need to stay in place well beyond the initial move, permanently in practice for a domain migration. Google’s Change of Address tool in Search Console is designed to carry signals from the old domain to the new one and continues applying that preference for a defined window after you initiate the move in Search Console, but the redirects themselves should remain live indefinitely, not just for that configured window, since old backlinks, bookmarks, and stale external references will continue pointing at old URLs indefinitely.
Parallel Search Console monitoring of both properties. Keep both the old and new domain properties active in Search Console throughout the transition and monitor them side by side, watching Coverage/indexing status, Core Web Vitals, and performance data on both. This lets you see whether traffic loss on the old domain is being matched by traffic gain on the new one (expected and healthy) versus traffic simply disappearing from both (a real problem requiring investigation), which is a distinction you cannot make by watching only one property.
Set stakeholder expectations honestly before the migration starts. Brief stakeholders in advance that some organic traffic trough during the transition period is expected at this scale, driven by the time Google’s infrastructure needs to recrawl and reprocess hundreds of thousands of URLs, and that this occurs even with a technically flawless migration. No credible source publishes a specific duration or depth figure tied to page count, so avoid promising a specific number of weeks or a specific percentage recovery timeline; commit instead to the process (staged rollout, continuous monitoring, rapid fixes to any section that underperforms) rather than a fixed number that cannot be responsibly guaranteed.
