Want the short answer? It depends on your business, but most guides won't tell you that honestly. They'll give you a percentage of revenue and leave you to work out what that actually means in pounds.
Here's a more useful way to think about it.
If you've got no marketing at all, start smaller than you think.
You don't need thousands a month to get moving. A clear website, a simple way for people to get in touch, and one channel you can stick to consistently will do more than a scattered effort across five platforms. £300-£500 a month is enough to make real progress if it's spent properly.
If you're already getting some enquiries, spend a bit more to grow steadily.
Once the basics are working, adding paid ads or proper SEO on top makes sense. This is usually where £500-£1,000 a month starts to show results, depending on your industry and how competitive it is locally.
If you're trying to grow quickly, you'll need to spend more.
There's no way around this one. More visibility costs more, whether that's ad spend, content, or someone's time managing it. But "more" should still mean spending well, not spending everywhere.
The number matters less than where it goes.
A tight budget spent on one or two things properly will always beat a bigger budget spread across everything at once. Before you increase spend, check the basics are solid: does your website actually explain what you do? Is there an easy way for people to get in touch? Are you showing up somewhere your customers already are?
If you're not sure where your money should go, that's usually the real question, not the number itself.
If you want a rough steer: I offer ongoing marketing support from £500 a month, scoped around what you actually need. If you want a second opinion on where your budget should be going, get in touch, and we can talk it through.