If you are part way through your current car lease and over your agreed mileage, then its alwaysbest to ring the leasing company and find out how much it would be at that point to increase your mileage. It doesn't always work out cheaper to take the increased rate. So make sure you do the math, calculate the estimated mileage, the difference in rental and what you'd pay if you handed the car back over the mileage allowance.