How many times have you forgotten when you last touched the keys to the car parked in your garage? It's quite common. One car is used daily, while the other might only be started once or twice a week, usually just for grocery shopping.

However, when you see the monthly expenses for insurance and registration piling up, you start to wonder if it's worth holding onto both cars. Instead of relying on feelings, I decided to look at the actual numbers.

In fact, it's not uncommon for households to own more than one car. According to data from the U.S. Census Bureau, 37 percent of all households own exactly two cars, and when you include those with three or more, nearly 60 percent of households have more than one vehicle.

A recent study by AAA found that the average annual cost of owning a new car is $12,863. Divided by 12 months, that's $1,071.92, which is an increase from last year.

This figure includes fuel costs, maintenance and tires, insurance, registration fees and various taxes, depreciation, and financing interest.

Breaking it down, depreciation is the largest expense, averaging $4,422 per year, which accounts for a significant portion of the total. What surprised me is that depreciation occurs regardless of whether you drive the car or not; it decreases over time.

Even if the car is just sitting in the garage, its value continues to drop. In fact, about 20 percent of its original price is lost within the first year, and nearly 55 percent after five years, indicating that depreciation happens much faster than expected.

Financing interest also averages around $1,184 per year. This interest includes the first-year costs for taxes and registration.

The average insurance cost for a safe driver is $2,098 per year. If you add a second car to the same insurance policy, it typically adds an average of $1,185, but this can vary significantly from $862 to $1,804 depending on the insurance company.

Fortunately, bundling two or more cars under one insurance policy can lead to discounts, ranging from 8 percent to 25 percent, with AAA offering discounts of up to 27.3 percent. Even with these discounts, the average savings is about $830 per year, meaning the insurance cost for the second car doesn't disappear entirely.

Ultimately, when you crunch the numbers, the answer becomes surprisingly clear. Fuel costs are about 17.3 cents per mile, and maintenance and tires are around 11.7 cents per mile, so for a car that's driven less, there are definite savings in these areas.

The problem is that fixed costs like depreciation, financing interest, basic insurance, and registration fees are much larger and don't depend on mileage. No matter how little you drive, these fixed costs will show up on your bill every month.

When I realized that I was spending over $100 a month on a car that was just sitting there, it made me feel conflicted. I understand the desire to keep it for convenience when needed.

But seeing the actual numbers showing that I was paying thousands of dollars in fixed costs each year changed my perspective. If I only drive it once or twice a week, I could easily use that money for Uber or a rental car instead.

I also looked into alternative costs. Car-sharing services like Zipcar charge a monthly fee of $7 to $8, with hourly rates around $9, which include gas, insurance, and maintenance, making it a much lighter option for occasional use.

If you only need an SUV or larger vehicle on weekends, personal car-sharing services like Turo can be a good option. Depending on the vehicle, daily rates can range from about $33 to $90, making it a much more economical choice if you only need it a few times a year.

Of course, there are situations where having two cars is genuinely necessary, such as when public transportation is lacking or when commuting routes are completely different. In those cases, this calculation doesn't apply.

If a child has just started driving or if a couple commutes in opposite directions, the situation changes. In such households, the second car will likely accumulate significant mileage, so the premise of it just sitting there doesn't hold.

On the other hand, if you have a car that's just sitting there, the timing of selling it becomes more important than you might think. Depreciation continues to occur, and the longer you wait, the less money you'll have in hand.

Additionally, selling one car not only stops the monthly fixed costs but also provides a lump sum of cash that can be invested elsewhere, which is an important consideration.

It's worth considering how to sell it as well. Trading it in directly with a dealer is convenient, but they often offer lower prices than the market value. If you have a little time, comparing offers from private sales or online buying services can yield a better return.

Personally, I would start by checking the driving records from the past three months. If the mileage on the second car is noticeably low, I would ask myself if I'm holding onto it for emotional reasons.

After reviewing the numbers, I concluded that it makes much more sense to sell one car and invest that money elsewhere rather than awkwardly maintaining two.