This is a question I get often. The answer is "It's complicated".
An answer that is very true is "15 years-- including all the practice paintings that didn't work out."
There are a lot of factors at play in determining how long a painting takes including:
Size- this may be a more obvious one that the larger the painting, the longer it takes. That is often true, but not always. No matter the size of the painting, the planning stages of the color palette and the composition takes more time and experimentation than you would tnink.
2. Complexity of subject matter- for example, a small 10x8 inch portrait will often take me much longer than a large impressionistic 24 x30 landscape painting. Humans are the most time-intensive. Landscape is usually more simple. Other complex subjects include buildings, vehicles, flowers, complex lighting, etc. The above painting is only 10x8, but I have spent several studio sessions working on it because of the complicated and subtle light effect.
3. Style- A large brush-stroke style that is nearly abstract CAN go quickly, but there are often do-overs involved. It's a high-risk venture! A more detailed realistic painting can take a very long time indeed, but in my opinion can lack the personality of the artist or character of the subject if no creative chances are taken.
4. Emotional State of the Artist- When I hear people say "painting is so therapeutic" it really sets my back up. Paint by numbers or paint and sip paintings? Heck yes! Very therapeutic! And I'm not belittling the importance of those in any way! But when you are doing all the creative from-scratch work, it's SO all-out energy sucking, (in the zone) that you have to be in a healthy and balanced state of mind and emotion to even start.
That being said, I love working to a deadline, and so far I have never needed more time than I quoted for my commissioned portraits and landscapes! If you like my style, but haven't quite picked out the painting in my collection that you would love on your walls, I encourage you to consider a custom portrait or landscape painting. Custom works start as small as 8x10 inches and go up to as large as you would like!
Visit www.adventurepainter.org or email me at firstname.lastname@example.org