Every self-employed professional who works on a project basis has had the experience of clients who need something “yesterday.” The small business client doesn’t contact her graphic designer about a flyer until a week before the trade show. Or, the taxpayer client doesn’t provide those missing documents to the accountant until a few days before the filing deadline. All of a sudden, these demanding clients expect you to magically do your job in half the time required, regardless of your other workload or your personal commitments.

As much as you’d like to please everyone, you can’t let your clients manage your business. Instead, you need to manage your clients. Often, this problem begins when a client makes an impossible request, and you drop everything to deliver what he or she needs. The client thinks you are a star, and gives you more business.

Because you were able to do it in record time once, the client doesn’t see any problem with asking for a 24-hour turnaround next time, either. Every time you meet clients’ unreasonable deadlines, you reinforce their expectation that you will continue to do so. Why should they bother to plan ahead if you manage to get it done for them anyway?

Don’t make the mistake of thinking that this method of operating is the best way to keep your clients happy. Not only will you end up grouchy and exhausted, but eventually, this strategy will backfire. When the day finally comes that you can’t meet the expected deadline, your client will feel let down.

To avoid getting into this situation, begin every client relationship with a discussion of expectations — yours and theirs. Let clients know your working hours, and how available you are for new projects. When a project depends on getting additional information from clients, tell them what lead time you need for those details to be provided. If you are currently under contract to another client for 20 hours a week, or you have a major project that will last another month, tell your clients about it. Professionals like you, who are good at what they do, are always in demand, so don’t be afraid that you will scare clients off by letting them know you are busy.

When it comes to examining the requirements for a particular project, remember that your clients hire you because you are the expert. It’s your job to tell them how long something will take — both in billable hours and elapsed time — and how much it will cost. You may need to educate them about everything that goes into your work, so they can see why preparation takes so many hours, or why an extra three days are required for the review cycle.

You and the client must agree together on the project’s due date. If the client insists on an earlier deadline, don’t say yes right away. Take the time to map out everything you have to do between now and then, including other client projects and your own priorities. If you’re sure you can get it done without losing too much sleep or letting more important things slide, then go ahead. But be sure to let clients know when you have to rearrange your other obligations to accommodate them.

When a client’s deadline is truly impossible, you just have to say no. Try putting it this way: “I can’t do that for you today, but I could have it done by tomorrow at 4:00.” Most clients will appreciate the promise of a firm deadline much more than when you say, “I’ll try,” and then can’t deliver.

Don’t be too concerned that you may lose clients to competitors if you insist on reasonable deadlines. Clients who refuse to allow sufficient time for their projects are always going to be difficult to work with. Let them go, and easier clients will take their place. If you really need the work right now, try charging a premium for rush jobs. The extra expense will sometimes bring a demanding client into line, and if not, at least you will get paid for the inconvenience.