Before answering the timeline question, it helps to be clear about what Domain Authority actually is, because the honest answer changes how you should think about the schedule.
Domain Authority is a third-party score, not a Google ranking factor
Domain Authority (DA) is a metric created and maintained by Moz, a third-party software company. It is a predictive score, on a 1 to 100 scale, that estimates how likely a website is to rank well in search results. It is calculated mostly from the number and quality of links pointing to a site.
Google does not use Domain Authority. Google has stated this directly more than once, and Moz itself has confirmed that DA is not a ranking signal in Google’s algorithm. The same is true of similar scores from other vendors, such as Domain Rating or Authority Score. These are useful estimates produced by analytics tools, but they are not the thing search engines actually measure.
This matters for your question. An SEO company cannot “improve your Domain Authority” the way it can fix a slow page or correct a broken tag, because DA is not a setting on your site. It is a third party’s calculation. What an SEO company can genuinely work on is the real-world thing DA tries to estimate: the strength and trustworthiness of the links and references pointing to your site. When those signals improve, your DA score usually rises later as a side effect.
What is realistically being improved, and when
The honest version of your question is this: when do link-based authority signals tend to strengthen? That follows a fairly predictable pattern.
First, an SEO company needs time to do the work. Earning quality links through outreach, digital PR, useful content, and genuine relationships is slow by nature. Expect the first few months of an engagement to produce groundwork rather than visible score changes.
Second, search engines need time to find and process new links. After a link goes live, a search engine has to crawl the linking page, index it, evaluate the relationship between the two sites, and filter the link through its spam and quality checks. This processing period commonly takes several weeks to a few months for a single link.
Third, third-party tools update on their own schedule. Moz recalculates Domain Authority periodically, so even after links are earned and processed, your DA number may not move until the next index refresh.
Putting those stages together, a reasonable expectation is that you may see authority signals begin to strengthen within roughly three to six months of consistent, quality work, with more meaningful movement over six to twelve months as links accumulate. The DA score itself often lags behind the underlying improvement.
What a trustworthy SEO company should tell you
Be cautious of any company that promises a specific DA score by a specific date, or that guarantees fast jumps in the number. Rapid increases are usually a sign of low-quality or purchased links, which can carry real risk and add no lasting value.
A reliable SEO company should explain that DA is an external estimate, set expectations in the range of months rather than weeks, and focus its reporting on outcomes that actually affect your business: relevant traffic, keyword visibility, the quality of sites linking to you, and conversions. DA can be tracked as one rough indicator among several, but it should not be the headline goal.
If you specifically want to know how an SEO company works to raise authority signals, that is covered in a companion article. The short version for timing: there is no exact date. Authority builds gradually through consistent, legitimate work, and the score that reflects it tends to follow a few months behind the work itself.