Forecast the cash around the payment terms, not the programme alone

The programme tells you when you spend; the payment terms tell you when you get paid, and the gap between them is where small contractors drown. Build the forecast from both: cost going out week by week off the programme, cash coming in off the application dates, the payment periods and the retention deductions the contract imposes. A forecast that assumes money arrives when the work is done, not a month or two later when the contract says it must be paid, will surprise you at the wrong moment.