Use this website to check whether any visits you make to Turkey satisfy the 90/180 day rule.

You can apply for an E-Visa using the link to the official Turkish Website. Beware of other sites which charge extra.

The KTLN Visa Article is well worth a read. Thanks to John at KTLN for the link.

From the menu on the left, you can read how the date calculations are made or check passport requirements .

Finally, you can contact me with any comments, queries or problems using the website.

Frequently asked questions

When can I go back to Turkey?

This is easy to answer because there is no definitive answer but it's quite tricky to explain.
If you are planning to go to Turkey, then you are probably not there at this time which means you left Turkey some time ago (could be a day, a week, 2 months etc.)
What is certain is that on the day you left, a 180 day period came to an end.
Today is 20th October 2017 so, as an example, let's say you last left Turkey 45 days ago on 5th September 2017.
When you left Turkey, the Immigration officers counted back 180 days to determine how many days you spent in Turkey during that period.
So, you left on 5th September 2017 and if we count back 180 days, it takes us back to 9th March 2017. You were allowed up to 90 days in Turkey during this time some of which were taken up by your visit which ended on 5th September 2017.
When you plan to return to Turkey, it's not when you go that's important, it's when you intend to leave. Let's say you want to go again next month on 21st November 2017 and leave two weeks later on 5th December 2017. There is now a new 180 day period to consider. Counting back 180 days from the day you intend to leave (5th December 2017)) takes us back to 8th June 2017.
Again, you are allowed 90 days between 8th June 2017 and 5th December 2017 but you've already used some on your earlier visits within this period - certainly the one that ended on 5th September 2017.
There is no easy answer I'm afraid. Use the Date Calculator and play around with the dates - it will warn you of any problems.

When do I get another 90 days?

You don't ever "get" 90 days - it's just the number of days you are allowed to spend in Turkey during any 180 day period (see above).

But the visa says 90 days up to its expiry date

You are not allowed 90 days per visa. The 90 out of 180 day rule always applies. Think of it this way.
If you bought a visa valid from 1st January to 30th June, you may think that this entitles you to 90 days in Turkey. It does!
If you then buy another visa valid from 1st July to the end of December, another 90 days right? - Wrong! (well sort of..)
This is one of the reasons the 90 out of 180 day rule was brought in.
In this example, on the first visa you could spend April, May and June - let's say 90 days - in Turkey before leaving. You would think that, as you have another visa, you could go back for July, August and September (another 90 days).
When you leave at the end of September and count back 180 days, you have been in Turkey for all of them (90 days on each visa). This is not allowed and you would be severely punished.
The visa should be regarded as a permit to be in the country rather than an entitlement to days.