13-week cash flow forecast: Excel or software?

I tell clients to build their 13-week cash flow forecast in Excel.

In a world where there's a new AI-powered finance tool launching every other week, recommending a spreadsheet sounds like old advice. But it's one of my core beliefs, and I'm going to explain exactly why. So if you are trying to decide if your 13 week cash flow forecast should be done in Excel or a software solution, then keep reading.

The software options are genuinely impressive

Let me be clear: the dedicated cash flow forecasting and treasury management platforms out there are excellent. Tools like Kyriba and HighRadius are sophisticated, powerful, and built for serious financial operations.

But here's the thing. They're built for very large businesses.

We're talking enterprise platforms with large price tags. Implementation timelines of several months (if you really want it tailored to your business), depending on the complexity of your bank, ERP, and payment system integrations. Dedicated customer success managers. Months of configuration before the tool is actually tailored to how your business works.

These are the right solutions if you're a business doing £500m or more in revenue, and probably closer to £1bn or above. At that scale, the investment makes sense. You've got the complexity, the volume, and the internal resources to implement and maintain it properly.

For most of the businesses I work with, that's not the situation.

13-week cash flow forecast: Excel or software?

The deeper problem with off-the-shelf software isn't just cost or complexity. It's that cashflow forecasting doesn't follow a standard template across businesses.

Every business has a different structure, different cash flow drivers, and different data sources. A one-size-fits-all platform struggles to account for all of that, and in my experience, it usually doesn't.

Here are some examples of what I mean.

A business that sells on credit terms will forecast its cash inflows using accounts receivable data: open invoices, due dates, expected collection timing. That's the logical source of information.

But a retail business collecting cash at the point of sale doesn't have that data. Its cash inflows need to be forecast from a sales forecast instead, which is a fundamentally different input and a different methodology.

A single-entity business can have one model that covers everything. A business with multiple entities across multiple countries needs a decentralised process: templates sent out to each business unit, inputs collected and consolidated centrally, with all the version control and coordination that involves.

A business using an invoice discounting facility can't just forecast cash inflows on a straightforward basis. It needs to monitor its available headroom on the facility, forecast drawdowns, and build that into the model as a distinct cash flow line.

I could keep going. The point is that the variability in how cash flows need to be built and modelled is enormous, and the businesses that need a 13-week cash flow forecast most urgently don't have the time or budget to spend months configuring a platform before it works for them.

Why excel works

Excel isn't the right answer because it's free (though it helps). It's the right answer because of what it can do.

It's completely flexible. You can build the model exactly the way your business needs it, using the data sources that are actually available, structured in a way that reflects how cash actually moves through the business.

There's no implementation timeline. You're not waiting for a customer success manager to configure your account. You can start building on day one.

Every finance professional already knows how to use it. There's no learning curve, no internal adoption challenge, and no training programme to run before anyone gets value from it.

And critically, when the business changes — a new entity is added, a facility is restructured, a new revenue stream comes in — you can change the model to reflect that without raising a support ticket.

The knock on Excel is that it's manual, error-prone, and difficult to manage across multiple users. That's true if the model is poorly built. A well-structured 13WCF in Excel, with clear inputs, logical flows, and a sensible update process, doesn't have those problems. The discipline matters more than the tool.

The tool isn't the hard part

Here's what I actually think the issue is.

Most businesses that don't have a working 13-week cash flow forecast aren't stuck because they haven't found the right software. They're stuck because they haven't built the right model, or they've built something that doesn't quite fit the way their cash flows work, or they don't have a consistent process for updating it.

The chances are that if you need a 13-week cash flow forecast, you already have the tools you need. Excel is almost certainly already there. What you might need is someone who's done this before, who can look at your specific business and build the right model for it, and who can save you the time and energy of figuring it all out from scratch.

That's a different problem from needing better software.

If you want to get started, grab my free 13-week cash flow forecast template. It's built in Excel and it's designed to be adapted to your business.

And if you'd like help thinking through how to set up the right model for your specific situation, I'm happy to have a conversation. I'd want to understand the detail first, but if it seems like I can help, we can move quickly.