If a vehicle is certified with a 100,000 mile bumper to bumper warranty for 4 years how much would that add to the buying price?

Depends on how much warranty is left, it will help your car stand out from the others and is a powerful selling tool.

Is it by the year or mileage or which ever comes first?

Lincoln Certification gives: 4 years left or 100,000 miles bumper to bumper warranty 1 year free maintenance 0.9% for 48 months vehicle has 23000 miles

Recently purchased a 2014 Lincoln CPO MKZ AWD 3.7 V-6 with 7,200 miles and we love it. The general manager showed me that the dealership has to pay $995 to certify a vehicle as CPO. Certainly the vehicle has to qualify by mileage, condition and has to pass intensive inspection. I would think the CPO would add somewhere between $1,000 and $2,500 to the value or price of the car. A Navigator CPO might even be worth more than the MKZ as the Navigator is a much more expensive vehicle.

Lincoln CPO is 6 years or 100,000 miles bumper to bumper with a small deductible. The 6 years starts when the vehicle was first placed in service when new. It is a great CPO plan.