My Prius

I own a 2006 Prius. In my actual usage of the car, it gets just about 45 miles per gallon. We are going to estimate how much money I save (if any).

But before we do that, note that actual usage can be different than the published EPA mileage numbers. For example, for the 2006 Prius, the EPA mileage for city driving is 60 miles per gallon, for highway driving is 51 miles per gallon, and for combined driving is 55 miles per gallon. In the computations below, we will use the actual miles per gallon that I get, which is 45 miles per gallon.

So how much money do I save on gas? Let’s compare my car with

1. Car A that (actually) gets 30 miles to the gallon and

2. Car B that (actually) gets 15 miles to the gallon.

Assume first that all three cars go 10,000 miles and gasoline costs $3.00 a gallon.

(Since I wrote the first draft of this post, the price of gasoline has started to come down. So I am going to include the results for $2.00 gallon gasoline in parentheses after the results for $3.00 per gallon gasoline.)

1. At 45 miles per gallon, my Prius uses 10,000 / 45 = 222.22 gallons. Since gas costs $3 per gallon, my cost is 222.22 * 3 = $666.66 (at $2.00 per gallon my cost is $444.44)

2. At 30 miles per gallon, Car A uses 10,000 / 30 = 333.33 gallons at a cost of $1,000 (a cost of $666.66)

3. At 15 miles per gallon Car B uses 666.67 gallons at a cost of $2,000 (a cost of $1,333.33)

So when I drive 10,000 miles,

1. Compared to Car A, I save $333.33 (I save $222.22)

2. Compared to Car B, I save $1,333.33 (I save $888.89)

Stated differently

1. Compared to Car A, I save 3 1/3 cents per mile (I save 2.22 cents per mile)

2. Compared to Car B, I save 13 1/3 cents per mile (I save 8.88 cents per mile)

Suppose I keep my Prius for 150,000 miles, which is the mileage my last Toyota had when I donated it to a charitable organization. My total savings over the life of my car would be

1. Compared with Car A, I would save $0.03333 * 150,000 = $5,000 (I would save $3,333)

2. Compared with Car B, I would save $0.13333 * 150,000 = $20.000 (I would save $13,333)

But did I really save anything when considering the extra cost of my car. After all, I certainly paid something extra for the hybrid mechanism. Taking that into account, did I save any money? It’s hard to determine how much I paid for the hybrid mechanism because Toyota doesn’t make a non-hybrid Prius. But they do make both a hybrid and a non-hybrid Camry. The base price for the 2007 hybrid Camry is $25,900, and the base price for the 2007 non-hybrid Camry is $18,445. Thus the base price for the non-hybrid Camry is 71.2% of the base price of the hybrid Camry. Using that same ratio and the base price of the (hybrid) Prius, which is $22,175, the base price of a non-hybrid Prius would be $15,788. Thus the extra cost I paid for the hybrid mechanism would be $6,387.

Hence, over the 150,000 mile estimated life of my Prius,

1. Compared with Car A (with mileage of 30 miles to the gallon), I would lose $1,387 (I would lose $3,054)

2. Compared with Car B (with mileage of 15 miles per gallon), I would gain $13,613 (I would gain $6,946)

However, I got a $3,145 income tax rebate for buying a 2006 Prius. Factoring that in

1. Compared with Car A, I would gain $1,758 (I would gain $91)

2. Compared with Car B, I would gain $16,758 (I would gain $10,071)

Suppose we consider a different car, Car C. How many miles per gallon would Car C have to get so that I would exactly break even after going 150,000 miles considering the cost of the hybrid mechanism (and ignoring my tax rebate)? A little math shows the answer to be about 27.5 miles per gallon (18.3 miles per gallon).

Now let’s consider a different question: what would gasoline have to cost so that the drivers of Car A and Car B would spend the same amount of money on gasoline to go 10,000 miles as I do in my Prius, $666.66 ($444.44). (Of course, the same price of gasoline would apply no matter how many miles we used in the computation.)

1. Since Car A used 333.33 gallons, gasoline would have to cost 666.66 / 333.33 = $2 per gallon ($1.33 per gallon)

2. Since Car B used 666.67 gallons, gasoline would have to cost 666.66 / 666.67 = $1 per gallon ($0.67 per gallon)

Unfortunately, I can remember when gasoline could be bought for all of these prices (and even cheaper).