This is, of course, one of those piece-of-string questions: Writing a novel will take just as long as it takes, no more and no less. There are just too many variables to put a definite timeframe on writing a long work of fiction...
Speaking of thin and fat novels, the first question I really need to tackle is how long a typical novel actually is.
The short answer is somewhere between 80,000 and 100,000 words. For the longer answer, please check out What Is the Ideal Novel Length?
Back to working out how long writing a novel will take...
If you search the Internet for writing guides (and I do that a lot - checking out the competition!) you frequently come across some course or program claiming to show you how to write a book in as little as 30 days.
If you write 3,000 words per day, the argument goes, you will have a 90,000 word novel sitting on your desk by the end of the month. Which is total garbage, of course.
Trouble is, a lot of new writers believe that it is technically feasible to write a novel in such a short time. After all...
That's what National Novel Writing Month is all about, isn't it? No, it's not actually - NaNoWriMo is about writing a first draft in 30 days. The organizers themselves are quick to point out that it takes a lot longer than a month to write a complete novel...
(Please read Can You Really Not Write a Novel In a Month? for more.)
Now, I am sure it is possible to write a novel in six months, maybe less if you really pushed yourself (and don't have the inconvenience of a living to earn). But I would think that 12 months is a more realistic minimum, and two to three years if you don't want to rush.
You don't become a doctor or a lawyer in a few months. You don't become an expert in anything in such a short space of time. So why would it be any different with writing fiction?
The answer is that they take anywhere from a few weeks (Barbara Cartland comes to mind) to the best part of a decade (I can't remember who off the top of my head, but I read an interview with a famous writer who had taken that long).
If a professional writer brings out a new book every year, they are said to be prolific. A new novel every two to three years seems to be about the average, with a four or five year gap not uncommon.
So where does that leave you?
Well, the thing to remember is that professional novelists, at least the famous ones, have the luxury of being able to write full-time.
(Yes, I know they do other stuff besides writing, like going on book tours and writing newspaper columns, but they still don't have a day job to go to.)
Also, they are good at what they do and have years of experience behind them - and the more we do something, the quicker and more efficiently we can do it.
If you are writing a novel for the first time and you do have a job, you have neither experience on your side nor plenty of hours in the day - meaning the two to three years I recommended as a comfortable target might not be quite so comfortable after all.
Only you know your circumstances and the particular novel you have in mind, and only you know if you are prolific or one of life's tortoises. So only you can make a guess at how long writing fiction to a publishable standard might take.
I'm just trying to warn you against setting unrealistic targets (or setting targets at all, actually). My best advice is to...
Write as often as you can, and be as productive as you can during your work sessions. But don't put added pressure on yourself with a ticking clock. It will only make you rush - and rushing is unlikely to make your novel better.
Above all, don't forget to enjoy yourself. Your livelihood doesn't depend on you finishing your novel to a deadline (at least, it shouldn't - making money from writing should never be your primary motivation).
In fact, the healthiest way for newcomers to view writing is like a hobby with prospects. And what is the point of a hobby if you forget to have fun?
Having said everything I have said above, I can fully appreciate that some of you will want to have a timeframe in mind before you set out on something as momentous as writing a book.
And so I have written an Outline For Writing a Novel in One Year, just to give you an idea. (Don't take it too literally, though.)
For me, though - and hopefully for you, too - rather than focusing on the finishing line by asking how long a novel takes to write, it is much better (and ultimately more productive) to decide how you will make the most of every writing session.
With this in mind, here are a couple more articles for you to check out...