An autism assessment appointment usually takes between one and four hours. From referral to results, it can take anywhere from four weeks privately to several years on the NHS.
However, timings do differ depending on the region, whether it’s a child or adult assessment and the pathway you choose. Knowing roughly how long you can expect an autism assessment to take at each stage means you can plan and choose the right route for you or your child.
In this blog, we’ll cover what happens at each stage, how long adult and child assessments take, how long the wait is on each pathway and why it can take so long.
What Are the Stages of an Autism Assessment?
There are four parts included in an autism assessment; understanding each of them gives a fuller picture of how long you can expect the whole process to take. The four stages are:
- Referral (NHS and Right to Choose only)
- Clinical interview
- Observation
- Feedback and written report
How Long Does Each Stage of the Autism Assessment Take?
Breaking down how long each stage of the autism assessment process can take builds a full picture of how long you could expect to wait from start to finish.
How Long Does Referral for an Autism Assessment Take?
Before you can have an autism assessment on the NHS, you first need a referral from your GP. Getting the referral can be quick, but the wait for the assessment itself is often much longer.
Guidelines set out by NICE state the wait time from referral to assessment should be no longer than 13 weeks (three months). However, in practice, most people wait much longer than that.
In parts of London, wait times for an autism assessment can be more than two years on average. For example, the wait time in Hounslow is currently two years, while Brent, Harrow and Hillingdon have waits of two and a half years.
Outside London, Greater Manchester has seen a rapid increase in the number of referrals, meaning the wait time can exceed seven years for some.
If you go through the Right to Choose pathway, wait times can be shorter, but it depends entirely on how busy the provider you choose is.
If you choose to go private, you skip the referral wait times, but there’s still a short wait of around two to four weeks for your appointment. Exactly how long you’ll have to wait depends on the provider you go with.
How Long Does the Autism Assessment Appointment Take?
The appointment itself is made up of a clinical interview and an observation. Before it, you’ll complete a pre-assessment questionnaire
The questionnaire typically takes at least an hour, though it can take longer depending on the provider and how much detail you put into your answers.
After this, you’ll have the clinical interview, which takes different amounts of time for adults and children. Adult interviews take between 60 and 90 minutes. For children, the full appointment can take up to four hours, as both the child and their parent or carer are interviewed.
Most assessments also include the Autism Diagnostic Observation Schedule (ADOS-2). During this step, a clinician will observe how you or your child communicate and interact through a set of activities. According to the NHS, this usually takes around an hour and forms part of the appointment.
How Long Does It Take to Receive Your Results From an Autism Assessment?
Many providers give initial feedback on the same day, no matter which pathway you take: NHS, Right to Choose or private. However, the actual report can take longer to arrive.
On the NHS, it can take a few weeks or even months for your diagnostic report to arrive. Wait times for results vary by region, depending on local demand.
For those who go with the Right to Choose pathway, wait times depend on the provider you choose, but they’re generally a bit quicker than the NHS.
As for private assessment results, these are usually delivered within a couple of weeks. Again, actual wait times depend largely on the provider.
How Long an Autism Assessment Takes From Start to Finish: Adult vs Child
How Long Does an Adult Autism Assessment Take?
In general, an adult autism assessment can take anywhere between a few weeks and several years, as capacity differs drastically between private and NHS assessments.
For an NHS adult autism assessment, you could be waiting as long as seven years from the initial GP appointment to receiving your diagnostic report. However, in regions with less demand, it may only be 12 months.
Private routes offer significantly shorter wait times, as they’re not working through the same referral backlog. In some cases, you may only have to wait six weeks from start to finish.
How Long Does a Child Autism Assessment Take?
Child autism assessments usually take longer than adult assessments, largely because of extra information gathering and longer waiting lists.
Unlike adult assessments, child autism assessments typically involve the child’s school. Clinicians will need to assess additional information provided by the child’s school when considering the results, which can mean the process takes longer.
Why Do Autism Assessments Take Such a Long Time?
Autism assessments can take much longer than the NICE guidelines set out for several reasons, ranging from demand for NHS services to the specific needs of the individual.
For the NHS, the long wait times for referrals make the whole process significantly longer than going private, but this is largely down to the high demand it faces. By the end of 2025, the NHS had more than 254,000 open autism referrals across England.
What’s more, the existing medical history of the person going for an assessment can impact how long it takes as well. It can take longer to reach a diagnosis for people with complex medical histories, as there are more factors for the clinician to assess and consider.
Similarly, it can take longer to reach a diagnosis for people with co-occurring conditions such as ADHD or anxiety, as the clinician needs to consider whether symptoms are linked to autism, another condition or both.
Lastly, clinicians rely on information from a variety of sources: friends, family, schools and employers. Waiting for feedback or forms can make the process longer, too.
There are steps you can take while you wait, such as keeping a journal of symptoms you notice to support your case when you do get an assessment. It’s important to note, too, that you don’t actually need a diagnosis to access support.
Children can access a SENCO in school, regardless of whether they have a diagnosis. For adults, you can reach out to support groups in your local area or speak to your GP about other options.
Get a Fast, Thorough Autism Assessment With NeuroAffinity
Here at NeuroAffinity, we provide fast, thorough autism assessments for both adults and children.
Our assessments are arranged within four weeks, getting you the answers you need when you need them. We use the same NICE guidelines and diagnostic criteria as the NHS, just without the lengthy wait times.
Get in touch with us today for more information. You can call us on 07768 565162, send an email to enquiries@neuroaffinity.co.uk or fill out our contact form for a callback.
Child ADHD Assessment FAQs
Is an online assessment faster than in person?
In some cases, yes, an online ADHD assessment can be faster than an in-person assessment. While the assessment itself will be the same length, you’ll save on travel time. For busy parents getting their child assessed, having no travel time can be the difference between booking and not booking an assessment.
What happens after an ADHD assessment?
After your assessment, you’ll likely receive some initial feedback. From there, your clinician will review their findings in more detail to create a full written report. If you’re diagnosed with ADHD, the report will likely include recommendations for support, too.
Does the NHS accept a private diagnosis?
In most cases, yes, as long as it was done by a qualified professional and followed NICE guidelines. However, GPs don’t always agree to prescribe ADHD medication when the diagnosis came from a private provider. Make sure to check whether your GP will agree to shared care before booking your private assessment. If they don’t, you may need to pay privately for your medication and reviews.
