That’s impossible to answer I’m afraid.
It’ll vary from person to person, much like writing does. Some people can write 50,000 words in a month, others might write 20,000 and some none at all.
The same goes with coding, depending on your mindset, experience and of course, what you actually want to code, it’ll take a varying amount of time.
You’ve also got different ways of coding, different methods of testing code and all that which will also add overlooked time onto your rate of production.
What I can say is that in a standard/typical game, writing and designing will be 80% of the game, coding being about 20%.
If you’re going for something a little more complicated script wise, like the late chapters of @JimD 's Zombie Exodus, @Vendetta 's Vendetta or @AlexCosarca 's Red Moon - It’s going to be more 50-50 and coding will begin to take up a huge chunk of your time, not least as you’ll often find yourself recoding a lot of different bits and bobs to get them to work exactly how you want them to.