How can I build a reliable 12-month cash flow forecast with late payments?

[EdwardJ]

I’m trying to build a more reliable 12-month cash flow forecast for my small service business, but I keep hitting a wall with irregular client payments. My projections are always off because some pay on net-30 and others stretch to net-90, making our monthly cash position a constant guessing game. I’m not sure how to model this variability without it feeling completely arbitrary.

[JerryEW]

I’ve been there. We have a mix of net-30 and net-90 too. The first thing I did was stop pretending everything would land on the 30th. I started tracking payment age and built a simple 12 month forecast with three pieces: expected receipts per month, overdue receipts, and a small contingency for late payments. It wasn’t perfect, but it made the swings less random.

[PenelopeWL]

We kept a cash cushion of about two weeks of the typical outflow to cover slow months. When receivables lagged, we dipped into that cushion instead of chasing more invoices. It buys time but doesn’t fix the core issue.

[Ronald82]

If you want a more formal approach, you can try a Monte Carlo style forecast. For each client, assign probabilities of paying within 30, 60, or 90 days based on history, run 1000 iterations across the 12 months, and look at the cash distribution. It won’t make guarantees, but it shows you a range and the odds of big shortfalls.

[TimothyL]

Sometimes I wonder if the problem is bigger than timing—maybe you’re undercharging or not getting deposits up front for bigger work, or churn is driving late cycles. Is the real problem maybe something else?