You're going to find a lot of (completely valid) advice on both sides -- bill by hour and bill by project. Out in the wild, there are a ton of factors that are going to make that advice either good or bad.

For example, the book, Million Dollar Consulting, is pretty famous for advocating the "charge by value" approach. I think a lot of what's stated in that book can make sense when you're 1) highly specialized and 2) are in high-demand. You have a lot more leverage in those situations and both sides of the equation likely know what value you're creating. These are the types of situations where managers inside the company you're working for are motivated to get through any red-tape your "non-standard" pricing models create.

However, in a lot of cases, businesses have policies and controls around how they structure contractor pay. You should certainly be flexible to not limit yourself, especially if you don't have a whole host of companies knocking at your inbox.

I'd suggest really thinking through how much time it takes to acquire (pitching, negotiations, other pre-contract meetings) a client, how much admin time it takes, and just build that into your hourly rate. Setting up retainer agreements is also usually a good idea for you and something clients don't typically balk at -- e.g. you will be paid a minimum of 10 hours per week, even if you only worked 5 hours.

For anyone worried about limiting their income by charging hourly rates, I'd suggest looking around at what high-end law firms, creative agencies, management consultants, accounting firms, etc. charge. As a solo consultant, you're ALWAYS going to be constrained by hour many hours you're willing to work, regardless of how you bill.

Per project or per time is one question, and yes - it depends on many things.

My point is that, from my experience, "per day" is strictly better than "per hour". In principle, you can say "just build it into your hourly rate". In practice, it is only if it is agreed beforehand how many hours, how distributed, and what is the non-billable overhead. Plus, adding conditions like "I am being paid for at least X h a week, I work in blocks of at least Y h, etc" , in my experience, added needless friction. I have learned to avoid the friction by saying "I don't have an hourly rate; my daily rate is X" and, if needed, adding that I am open to splitting some days in half.

> You should certainly be flexible to not limit yourself, especially if you don't have a whole host of companies knocking at your inbox.

I hope "you should" is rhetorical - I know what I am doing. Sure, there is a balance between how many clients are interested and how well I set conditions of collaboration with them. Obviously, in terms of when you set the balance, YMMV.

> For anyone worried about limiting their income by charging hourly rates, I'd suggest looking around at what high-end law firms, creative agencies, management consultants, accounting firms, etc. charge.

Agencies work on a very different basis than solo freelancers/contractors, including (but not limited to) the fact that on the bill, there are hours of many people involved.

> My point is that, from my experience, "per day" is strictly better than "per hour".

This seems to be a popular and strongly-held opinion on every thread about consulting on HN, but I don’t get it. If I spend 12 hours on-site with a client, I bill them 12 hours, not 1 day. If I decide to take a couple of hours off to walk the cat, I don’t bill the time and don’t feel guilty.