You don’t need calculus to forecast cash. Most ecommerce owners manage cash by checking the bank balance and making a judgment call. That works until it doesn’t.

A simple cash forecast starts with two lists: what’s coming in over the next 13 weeks, and what’s going out. Revenue from sales, marketplace disbursements, any pending payments owed to you. Against that: inventory orders, platform fees, payroll, ad spend, subscriptions, loan payments.

The goal isn’t precision. The goal is visibility. When you can see four to six weeks ahead, you stop being surprised. You know a gap is coming in week 8, so you plan for it now — instead of scrambling when it arrives.

Build the forecast in a simple spreadsheet. Update it weekly. It doesn’t need to be perfect to be useful. A rough map of the next 13 weeks is worth more than no map at all.