Does this mean you only work on one project at a time? I seem to maximize my billable time by doing one project at 20 hours/week plus a few long-term relationships with smaller ad hoc projects. Sometimes the "big" projects overlap briefly but I try to avoid that.

If I moved to weekly billing, I'm afraid I'd need a longer sales process and I'd have to turn down a lot of work that I can slip in with my current approach. So I'm curious: do you work one engagement at a time, and what is your time between engagements?

The only thing we're telling you not to do is to break your bills out by the hour. A whole lot of bad stuff happens when you start billing in sub-day increments.

How precisely do you specify upfront what a 'day' means? Are you just keeping it vague and not working with anyone who takes issue with that? Or are you specifying it as 6 hours so you have time to handle other things?

I recently attempted a move to daily billing but had a client who was anal about 1 day = 8 hours and this caused significant friction/lack of flexibility. The client was a somewhat difficult/overly-controlling person but willing to pay well for quality. Would you simply turn down someone like this?

I think that with all sane clients, you will also find that once the delivery date is negotiated to both sides satisfaction, nobody gives a shit about what happens in the intervening days. Good clients are happy to know that they're going to get something on a specific date. They are thrilled to have a black box that they can put money into and get value out of. Don't open up the black box and explain it. They don't need to know how the fuel injectors work, and if you explain electronic fuel injection to them, some of them will just get neurotic about whether it's functioning correctly.

I don't. All my recent contracts of this nature have simply stated that a day on which any services are provided is chargeable, or words roughly equivalent to that.

This does require a client to trust that I won't abuse the deal by, say, charging for a day off just because I spent a few minutes replying to an e-mail. I suppose legally speaking I could do that, but then legally speaking a client can typically also fire me in the time it takes to get a letter delivered if they're not happy with progress on their project. As with so much of this business, trust goes both ways.

In reality, I have never found this to be a problem. As others have said, clients are typically more interested in the value of the work you produce than in how, when, or where you produce it. You might see the occasional raised eyebrow if someone asks directly and is surprised at your answer, but personally I'm not aware that I've ever lost business or left unhappy clients over it.

The client was a somewhat difficult/overly-controlling person but willing to pay well for quality. Would you simply turn down someone like this?

Given a reasonable alternative, which is usually the case: yes.

Incidentally, in the UK, where I am, you should be very wary of taking on "overly controlling clients". If you aren't sufficiently independent -- as demonstrated by signals like your clients controlling your working hours -- then you could be deemed a disguised employee rather than a separate business. That leaves you with all the overheads of running a business, yet also leaves both you and your client with all the tax obligations of an employer-employee relationship, which is a Very Bad Idea.

This is a problem a couple friends of mine have had. It seems like incorporation, which is cheap and something you should do anyways, mostly fixes it.

In the UK, we have almost the opposite problem.

If you set up a limited company to operate a freelance business, then by default you get to run it like any other business. That means you're responsible for paying your own overheads and doing the same administrative paperwork and taxes as any other company. (Who else is going to pay for or do those things, after all?) However, it also means that if you're the only owner and director, you can treat most of the profits as dividends rather than salary, which can be a significant tax advantage in some quite common circumstances.

Unfortunately, this arrangement was being abused by some people who were in effect working as employees of someone else, who operated with little meaningful independence but were being paid through a company so they could take the tax breaks anyway.

Consequently, with probably good intentions but unfortunately not a very good implementation, a set of rules known as IR35 were introduced that basically said if your arrangement works like employment, you'll have to treat your contract like employment, with the full tax liability that goes with it.

The trouble is that there has never been any useful, objective definition of what counts as working like employment, so all we really have to go on are a few precedents from early cases. In practice, this means every independent professional here who works this way, however legitimately, has this permanent axe hanging over their head. You can pay some accountants for an expert contract review that comes with insurance if they tell you you're OK and you are subsequently determined to be within the scope of IR35 anyway, but that's a lot of hassle and a significant cost if you do change contracts often, so not everyone does.

The tax authorities did make an attempt to codify some more concrete guidelines with their Business Entity Tests a few years ago; those were supposed to give you a clearer idea of how likely you were to fall within the scope of IR35, but the questions were bizarre and completely ignored most of the really important distinctions between an employee and a genuinely independent professional operating as a real one-person company, and the BETs were effectively killed off not so long after they were introduced.

This leaves us back at square one. Despite protests from the independent sector about the ongoing burden of IR35 and the lack of evidence that it has ever generated anywhere near the kind of additional tax revenues it was supposed to, successive governments have maintained the rules arguing that if they removed them now then the floodgates would open and suddenly everyone would be going down the disguised employment path costing the government a fortune.

In practice, the good news for genuinely independent professionals is that the tax authorities have very limited resources to go after small time tax dodgers, so as long as you're behaving reasonably it seems you're unlikely to get in much trouble. This brings me back to where I came in, which is a warning that if you really are trying to operate properly as an independent, a very controlling client who is able to impose obvious restrictions like setting working hours is not something you want pushing you to the top of the pile for an IR35 investigation.

I wrote a fuller explanation here: http://digitalassassin.net/2014/07/am-i-caught-by-ir35/

To be clear, I'm not arguing that this is necessarily due to any ill intent on their part. It's just that even if HMRC people are trying to help when you call them, they can still fail to understand what the tax rules actually say and they can give incorrect advice as a result. When that happens, they seem to err on the side of saying you're caught by whatever it is you're asking about and should pay the extra tax.

If I'd taken them at their word the last couple of times I called, my companies would have paid far more tax than we really owed. (To be clear again, I'm not talking about any funny tax avoidance measures here, just applying the normal but somewhat complicated rules for things like international sales.) Fortunately, we also spoke with some accountants who could explain why the first advice was wrong, which in fact they did by citing parts of HMRC's own written guidance that HMRC's own people had overlooked.

I suppose this only matters if the clients vocalize this assumption?

I should probably point out that "maximising my billable time" isn't really an important goal for me as a freelancer, so we're likely talking about a different business model. You'll hear this a lot from patio11 and tptacek, but overwhelmingly, my goal is to provide as much business value to my clients as possible and charge accordingly.

You don't necessarily have to position yourself as a content marketing/CRO/Security/Sandwich-making consultant to do this, just find a way to make or save your clients buckets of cash and you can charge them whatever you want.

*: That makes me sound like some sort of rockstar freelancer, but in reality I'm a boringly average Rails developer. I get and keep clients by working really hard on sales and treating existing, long-term clients like my family's financial security depends on them (hint: it does!).