People ask this question like there's a number that applies to everyone. There isn't. But a few things I've learned about how long books actually take:
The range between real authors is so wide it's almost useless
If you go looking for data on how long it takes to write a book, you'll find numbers so far apart they stop meaning anything. Jack Kerouac typed the manuscript of On the Road in three weeks, feeding a continuous scroll of teletype paper through his typewriter so he wouldn't have to stop and reload pages. Donna Tartt spent ten years on The Secret History. Tolkien worked on The Lord of the Rings for twelve years while holding down a full-time professorship at Oxford. These are all real timelines for real books, and the spread between them is so enormous that averaging them out would be like averaging the price of a Honda Civic and a private jet and calling it a useful number for car shoppers.
The more interesting pattern is what was happening on a daily level. Ian Fleming wrote each James Bond novel in roughly two months, which sounds superhuman until you look at the conditions he set up. Every January and February, he'd go to Goldeneye, his house in Jamaica, and write from about 9 a.m. to noon. Around 2,000 words before lunch. No exceptions, no off days, no waiting for the mood to strike. Then he'd swim, snorkel, have drinks, and not think about the book again until the next morning. He did this fourteen times and produced fourteen novels.
What Fleming understood, probably without framing it this way, is that speed comes from removing decisions. He didn't deliberate about when to write or how much to write or whether today felt like a writing day. He'd already answered those questions once, permanently, and then he just executed the routine in a place with no distractions. The books weren't rushed. Casino Royale, Dr. No, From Russia with Love, these hold up. The consistency didn't make the work worse. If anything, it made the work more confident, because Fleming was always warm, always mid-stride, never starting cold after a three-week gap.
So when someone says "a book takes six months to two years," what they're really describing is the range of outcomes produced by different daily habits applied over time. The calendar doesn't write the book. The morning does.
First books take longer because you're learning two things at once
Your first novel takes longer for a reason nobody talks about enough: you're simultaneously writing a book and learning how to write a book. These are two separate skills happening in the same hours, and they compete for your attention in ways you can't fully anticipate.
Every first-time novelist hits problems they didn't know were problems. You're sixty pages in before you realize your point-of-view shifts are confusing, or that a subplot you loved in your outline has been wandering for forty pages without connecting to anything. Timeline inconsistencies creep in. Characters who seemed distinct in your head start blending on the page. These aren't signs of failure. They're the curriculum. But they slow you down because you have to both diagnose the issue and figure out the fix, often without any framework for either. Khaled Hosseini spent two and a half years writing The Kite Runner, his first novel. His second, A Thousand Splendid Suns, took about eighteen months. The gap wasn't because the second book was simpler. It was because Hosseini had already learned how scenes connect, how to manage a dual timeline, how to feel when a chapter was pulling its weight and when it wasn't.
It's a bit like learning to cook by hosting a dinner party. You're not just learning knife skills and how long to roast a chicken. You're also learning how to time five dishes so everything lands on the table warm, how to recover when the sauce breaks, how to adjust mid-stream when you realize you're out of an ingredient. The second dinner party is faster not because you became a better chopper, but because you learned all the invisible coordination that sits on top of the cooking itself. First books work the same way.