Model retention as cash you will not see for a year

Retention deducted each month is real cash leaving the forecast, and half of it does not come back until long after the job finishes. Contractors who ignore it are startled twice: by how much the monthly deductions tighten the job while it runs, and by how long the second release takes to arrive. Put every deduction into the forecast as an outflow and every release on its true trigger date, usually far to the right.