I recently spent an afternoon estimating how long I might live, using a few life expectancy calculators. It was this actuary’s idea of fun!

It was also very enlightening and sobering, even for someone who works researches and writes about longevity topics. It reinforced the conclusion that I should be planning for a long retirement, as should most people who are currently transitioning into retirement.

To help determine how long you might live, online calculators typically ask questions about your circumstances, health status, and family history. The more questions a calculator asks, the more personalized your life expectancy estimate will be.

The results you’ll get from the various online life expectancy calculators will likely be different, which illustrates that life expectancy calculations are an inexact science. There can be many influences on your lifespan, and there’s a great deal of uncertainty about exactly how long an individual might live, given their unique set of influences.

Despite this uncertainty, however, a life expectancy calculator is a good tool to help you get a ballpark idea of how long you might live, and that’s what I was hoping to find. I started with a popular life expectancy calculator, Livingto100.com, which was developed by Dr. Thomas Perls, a respected physician who wrote the excellent book Living to 100. This calculator is highly personalized, asking dozens of questions about your health, nutrition, lifestyle, and family history. It took several minutes for me to answer all the questions—a bit of a tradeoff between personalization and ease of use. But that calculator estimated I might live to age 101!  I didn’t believe the results, so I thought I’d try other calculators.

Next, I tried an easy-to-use life expectancy calculator offered by Northwest Mutual. It asked me 13 questions about my lifestyle and family history, and it estimated that I might live to age 100.

Then I tried a life expectancy calculator that was developed by professors at the University of Pennsylvania. It asked 14 questions about my health and lifestyle, and estimated that I would live to age 98, with a three in four chance I would live to at least age 90.

So far, the results from these three calculators look encouraging. However, none of my male ancestors lived until age 90, which gave me pause. To help temper my optimism, I used the Actuaries Longevity Illustrator, developed by the American Academy of Actuaries and Society of Actuaries. It’s the least personalized of the calculators I used, asking only questions about my overall health status and whether I smoke. It shows the odds of living to various ages, and if you’re married or have a life partner, it illustrates how long one of you might live. This is very helpful for retirees who want plan for the financial security of their spouse or partner after they’re gone. This calculator showed that there’s less than a 50/50 chance I’ll make it until age 90, and only a 7 percent chance I’ll live to age 100.

It was enlightening to see all the questions that the calculators asked, which provided insight into the factors that influence my lifespan. The different results also illustrated that there’s a lot of uncertainty surrounding how long I might live.

From the perspective of this 70-year-old, it seems that I could live another 20 to 30 years. The range of possible results demonstrates that I should plan to be financially secure no matter how long I live. It’s sobering to realize that a lot can happen in the world and in my community over such a long period. Think of all the changes that have happened in the past 20 to 30 years! So, I need to be flexible and be prepared to change my plans to keep up with the times.

On the positive side, I realized that I most likely have a lot of life ahead of me! It inspired me to be conscious about the activities I participate in and the people I choose to be around.

I strongly encourage you to try a few life expectancy calculators, review whether your financial plans support your expected lifespan, and reflect on the best use of the remaining time you have on Earth.