How the calculation works
Billable detention is total facility time minus the free-time allowance, never below zero. The result is then multiplied by the hourly rate. If your Rate Con uses billing increments or a cap, those terms can change the invoice amount.
What the calculator cannot tell you
A number is only useful if the load qualifies. Check notice rules, signed in/out time requirements, tracking, broker approval and any stated cap in the actual Rate Con.