It's normal to get different speed results when testing your internet connection during different times of the day.

You may see a slower speed in the evening for example, when there are likely to be lots of people using the internet.

Depending on your internet provider and your BT Exchange there may be some congestion or speed capping occurring.

To get the best results try running the speed test at different times of the day - mid-morning during the week will often show the best speeds your connection can get.

Your choice of ADSL Router can also have an effect on your internet connection speed.

BT Wholesale Broadband Performance Test - Broadband Diagnostic Test

IP PROFILE - the only official way to find your current IP Profile
BT Speedtester (BT's Official broadband speed test)

If you are on ADSL/ADSL2+/VDSL/FTTC (adaptive ADSL) to see your current IP Profile (also known as BRAS profile) you have to use the official BT Speedtester.

Change of address for the official BT speedtest
Originally www.speedtester.bt.com this has been replaced with speedtest.btwholesale.com

Shortcut: Rather than go through BT's first speed test to get to the 'Further Diagnostics' option to view your current IP Profile you can visit:
www.speedtest.btwholesale.com/PerformanceTesterWS/diagnostics.do
2020: This shortcut no longer works. To see your IP Profile use the main link above and run a normal test, then click the 'Additional Diagnostic' link to run a test which will display the download and upload IP Profiles.

BT used to require people to have Adobe FLASH installed - changes in 2019 mean FLASH is no longer required, this also means you can run it on your phone/tablet/Android etc. which can be useful.

NOTE: January 2020: The BT speedtest has always been a bit flaky when trying to view your line's IP Profile but recent changes seem to have made this situation worse!
UPDATE Oct 2020. BT IP Profile data availability seems to have improved and is currently working.

Some providers don't use BT's IP Profile system

For those on non-BT lines (TalkTalk, DAISY or Digital Wholesale Solutions as they are now) the equivalent official line test is www.supportal-test.co.uk

IMPROVING
INTERNET
SPEEDS

Errors running BT's speed test
 
Note: The BT Speedtester is famous for being rather flakey!
 
You may have to try running the test a few times before it runs successfully. Using a different browser can also help.
 
If you are trying to report a broadband speed problem then your ISP will normally ask you to use the BT Speedtester as this is the only official test BT will accept.

In January 2013 BT changed the URL for their official broadband speed test - see above.

The new test initially just does a simple Download, Upload and Ping Latency test - you can then follow the "Further Diagnostics" link at the bottom of the page which will ask for your phone number and then perform a speedtest which will display your IP Profile and maximum achievable speed.

BROADBAND CONNECTION HEALTH
If you are interested in finding out/monitoring your IP Profile for your own interest and not necessarily to report a problem then running the simple speed test above can show you this.

Once you start to understand your broadband lines' characteristics it's quite simple. See my ADSL information page for details. If your IP Profile is normal for your line then you know that any slow down is likely to be temporary due to external factors - a big sporting event etc. rather than your line having a fault.

SUPERFAST/FIBRE update:

If you are on a FTTC/Fibre connection using a BT supplied modem then line statistics aren't easily available - monitoring your IP Profile is a good way to see if your broadband connection is running normally.

For example. My line normally sync's (connects) at around 6,100kbps. That means the highest IP Profile I can achieve is 5000. So if I run the simple speed test above (no login etc. required) and see a download speed of say 4838 - then I know my IP Profile hasn't dropped and I'm on the highest I can expect on my line and everything is running fine with no throttling or speed limiting/congestion problems.