Should you really keep your XML sitemap lastmod dates up to date?

The lastmod signal in XML sitemaps tells Google the last modification date of a page. Contrary to what many believe, Google does not process this signal progressively or with nuance.

Gary Illyes confirmed that Google adopts a binary approach: either the search engine fully trusts your lastmod dates, or it ignores them completely. There is no middle ground.

This decision to trust or distrust builds over time. If Google detects repeated inconsistencies between your lastmod dates and the actual modifications to your pages, it will gradually stop using this signal to prioritize its crawling.

• The lastmod signal is treated in a binary way: complete trust or complete ignorance
• Incorrect or misleading dates can lead to permanent ignorance of the signal
• This directly impacts crawl prioritization and indexing speed
• Loss of trust can extend to the entire sitemap

This statement confirms what many SEO practitioners have observed for years. Sites that maintain fanciful lastmod dates do indeed see their important pages crawled less quickly.

However, this needs to be nuanced: this rule mainly applies to high-volume sites. For a small 50-page site crawled daily, the impact remains marginal. On the other hand, for e-commerce sites, media outlets, or directories with thousands of pages, it's critical.

The question is not whether Google uses lastmod or not, but rather how long it will grant you its trust if you mislead it. Once lost, this trust is difficult to regain.

• Audit your current sitemaps to identify inconsistencies between lastmod dates and actual modifications
• Configure your CMS to only update the lastmod when there are substantial content modifications (not for comments, views, etc.)
• Test whether your lastmod dates match real updates by comparing with publication dates and archives
• Consider removing the lastmod tag entirely if you cannot guarantee its accuracy
• Monitor crawl logs to verify that Google is properly prioritizing your recently modified pages
• Document your lastmod update logic to maintain consistency over time
• For multi-author sites, establish a clear workflow defining what constitutes a modification worthy of lastmod

Rigorous management of XML sitemaps and their technical signals can quickly become complex, particularly for high-volume sites or platforms using multiple CMSs. If you experience difficulties maintaining this consistency or if you want to optimize your crawl strategy holistically, working with a specialized SEO agency can help you implement the right practices and necessary automations to durably preserve Google's trust in your technical signals.