How long do eyelash extensions usually last?

Hi Charley.
I agree with the other answers but would like to say that eyelash extensions do need a lot of tlc to keep them on for more than 2 weeks. All your eye products needs to be oil free. Soap, cleanser, makeup, mascara, etc, and definitely no scrubbing! Anything with any oil in will eventually break down the adhesive and you will still need to wear mascara. They are very delicate and need to be treated that way.
Your own eyelashes also determine how long the lashes stay on as they are individually glued to your own eyelash. (Some people just can't have them as their eyelashes are too short or too curly). They can last up to 6 weeks but you would only be left with the odd few by that time. Don't forget that eyelashes, like any hair, shed. Infill treatments every 2-3 weeks are a must unless you're just having them for a special occasion.
This probably doesn't sell them very well but I don't get repeat customers if I'm not completely honest with them.
Initially they do look fab, and with infill treatments they can keep on looking fab.
Your specialist should stock oil free products for your aftercare.
Hope this helps :-)
Sarah

Eyelash extensions are not like the ones you buy in stores and apply yourself. When properly applied they are very hard to tell that they are not real. You should make sure they are using a medical grade adhesive and that they are applied no closer than 1 to 2mm from your eyelid skin (or they will cause irritation). They make your eyes look incredible. Some of the drawbacks include no more rubbing your eyes, touch ups every 2 to 4 weeks, no mashing your face into your pillow etc. You can swim but you cannot keep your face in the water for prolong amounts of time or your eyelashes will absorb water and the glue bond can "pop". I would suggest goggles if you are a frequent swimmer. http://tiny.cc/43gaqx

The longevity of an initial Lash Extension Application depends on
1] The Adhesive Used (professional is, of course, longer lasting)
2] Client Homecare (obvious care is required, mascara not advised)
3] Type of Lash (single, cluster, strip)
With professional adhesive and accurate application an extension should actually last for the duration of the natural lash cycle (ie permanent) ... However this could be anything from 1 day (if the natural lash is in it's final cycle of life or telogen stage) or as long as 6 weeks depending on your 'own' natural lash cycle and at what point during the early life cycle (or anagen stage) of your natural lash that the extension is applied.
Be warned that natural lashes are constantly going through a 'growth and shedding' cycle therefore the initial set of lash extensions that you have applied shall look their very best throughout the first week but will, over time, begin to look worn sparse.
Salons often claim that a set of extensions can lasts for up to 2 months however they must also explain that frequent (fortnightly) infil or 'maintenance' sessions are required whereby the salon replaces extensions that have naturally shed (usually for a lower fee than application) to maintain their 'fullness'
Alternatively you can return to the salon and have them professionally removed (with the correct solvent) if you no longer wish to have them on or 'topped-up'. It is very important to use the appropriate solvent during removal as other (less effective) methods can end up with you plucking the natural lash out along with the stubborn extensions that won't budge. This leaves you with gaps in your lashline that look odd when you come to apply mascara.
ALSO ... extensions need natural lashes to 'stick to' so if you accidently pluck any natural lashes out prematurely --- you'll be sad that you did!!