I received a request a couple weeks ago to convert a batch of mock-ups my client had already signed off on to the PDF format, so that its Dev team could more easily port marketing page copy into their page-coding project.

Due to some versioning issues on my end, the chore took about an hour. No big deal. You always want to keep your client happy, and in addition to being a promising customer, my contact also happens to be a long-time professional associate and a good friend. So, I knocked out the little request with no thought of an extra billing for the time. Obviously, it was the thing to do.

However, the situation got me thinking: How much time on post-final invoice tasks like this can you afford to absorb before you must let your client know that you need to bill them for your troubles?

It’s a little trickier than simply putting in a change order; theoretically, the project is closed. You’ve got sign off, and you’ve sent your last invoice. Most Accounting departments get a little irritable over invoices for a couple hours work, and even more irritable for additional billing for a line they think should be closed. So, that argues for just eating a few hours here and there, assuming you want to hold onto the client.

On the other hand, a few hours here and there can quickly mount to a sizeable chunk of lost billables. And once you give in a couple times, it’s like you’ve fed a stray cat – the requests keep on coming. It’s not just a question of a few bucks. Hopefully, you’ve moved on to a new project and have something better to do than re-wrangle a few details you thought (and been assured by your client) were already locked down.

I’ve found this phenomenon is most common if you are working on a component of an overall project that then gets passed on to another consultant or client team. As a VP of product development, I used to torment our outsourced design shop with after-close requests for color changes and other nominal tweaks. I thought the SOW was closed; my consultant thought the SOW was closed. But some new voice in the project (often C-level) suddenly sprouted a passion for “hot” colors, so back to the design shop I went. Often.

So, how many hours should you eat on these little requests, and how can you avoid them in the first place?

My rule of thumb is that if you are billing more than 40 hours on a project, you should build in at least an hour (on you, most likely) for a detailed close meeting before sending that final invoice. Although you can’t envision every quirky request a client might make, take the lead in anticipating weird little afterthoughts that might not have been covered. Experience will be your guide here.

After the close meeting, be ready to eat about three hours max of trickle-in requests gratis before you tell the client that you will need to open a new billing cycle for the effort. If your team has delivered a 300-hour soup-to-nuts solution, this hour count will vary. And you should already have built a shake-out and maintenance schedule into your agreement that, hopefully, will cover any unexpected events without raising Accounting’s ire.

But regardless of project size, you can’t let small “favor” requests continue to drag on forever. Because they will.