I will tell you everything from my experience of living here, and you decide when it will be more comfortable for you.

April:

Early in the morning and in the evening it is still cool.
During the day the air temperature is 20-23 degrees.
Water 17-19 (I think it’s cool for swimming)
Favorable prices for accommodation, hotels and excursions, which are very comfortable to visit in such weather.

May:

There is no strong summer heat yet, so the month is ideal for those who do not tolerate it well.
The air temperature is 24-26 degrees, and the water is already warmed up to 21 degrees and is suitable for comfortable swimming😍

June:

It is already hotter and the temperature is 28-31 degrees, the water is ideal for swimming, but there are already a lot of tourists and the prices for everything are growing noticeably.

July – August:

Hottest months, very warm bathing water (some say not refreshing at all).
Do not walk for a long time during the day, high humidity.

September:

Already better, the temperature drops to a comfortable June temperature of 28-31 degrees.
The sea is warm, slightly refreshing.

October:

It is also a very comfortable month for excursions and for swimming. The water in the sea is still warm + 23-24 degrees. And there is no sweltering heat outside. Read more about visiting Istanbul in October

November:

This month, the swimming season officially ends (we swim until +-20 November, if there is no strong wind). Very profitable tours. You can relax in a good 5-ke 🌟 2-3 times cheaper than in the season itself. Read more about visiting Istanbul in November

What month do you like to visit Turkey?☀️