There's a line people like to repeat: you spend a third of your life asleep. It sounds like one of those made-up facts, but it's really just division. Eight hours is a third of a day, so if you sleep eight hours a night, a third of your life goes to sleep.
The same simple maths works for screen time, and that one is usually the bigger surprise. This guide shows how to work out both numbers yourself, with examples for different ages, and what the Life Stats Calculator on this site does with them.
Quick answer
Take your average hours of sleep per night, divide by 24, and multiply by your age. That's roughly how many years you have spent asleep. Do the same with your daily screen time to see how many years you would have spent on screens if you had always used them as much as you do now.
For example, someone who is 25 and sleeps 7 hours a night: 7 ÷ 24 × 25 ≈ 7.3 years asleep.
The maths, step by step
There is only one idea here: a habit you repeat every day takes the same share of your whole life as it takes of a single day.
- Find the share of the day. Hours per day ÷ 24. Seven hours of sleep is 7 ÷ 24 ≈ 0.29, or 29% of each day.
- Multiply by your age in years. 0.29 × 25 years ≈ 7.3 years.
- Or work in hours. Multiply your hours per day by 365 to get hours per year. Seven hours a night is 2,555 hours of sleep a year. A year has 8,760 hours (365 × 24), so dividing by 8,760 turns hours back into years.
That's all the calculator does too, just faster and to the exact day.
Years asleep, by age and sleep habit
These are worked out with the formula above (hours ÷ 24 × age), rounded to one decimal place:
| Age | 6 hours a night | 7 hours a night | 8 hours a night |
|---|---|---|---|
| 18 | 4.5 years | 5.3 years | 6.0 years |
| 25 | 6.3 years | 7.3 years | 8.3 years |
| 30 | 7.5 years | 8.8 years | 10.0 years |
| 40 | 10.0 years | 11.7 years | 13.3 years |
| 60 | 15.0 years | 17.5 years | 20.0 years |
Real life is messier than a table. Babies and children sleep far more than adults, so if you're 25, your real number is almost certainly higher than the one in the table. Treat these as a floor, not an exact count.
Is that too much sleep, or not enough?
Neither. Sleep isn't wasted time. It's when your body and brain recover. The US Centers for Disease Control and Prevention (CDC) recommends:
- Children aged 6 to 12: 9 to 12 hours
- Teenagers aged 13 to 17: 8 to 10 hours
- Adults aged 18 to 60: 7 or more hours
- Adults aged 61 to 64: 7 to 9 hours
- Adults aged 65 and over: 7 to 8 hours
So if your number of "years asleep" looks big, that's usually a good sign. If you're an adult sleeping five or six hours most nights, the more useful thing to notice is the gap between what you get and what's recommended. This is general information, not medical advice; if you're worried about your sleep, talk to a doctor.
Screen time: the number that surprises people
Screen time works the same way, but most of us underestimate our daily figure. Your phone's own settings (Screen Time on iPhone, Digital Wellbeing on Android) show your real average, and it's worth checking before you do the maths. Remember to add laptop and TV time if you want the full picture.
Here's what different daily amounts add up to, using hours per day × 365:
| Screen time per day | Hours per year | Days per year | Over 10 years |
|---|---|---|---|
| 2 hours | 730 | about 30 days | about 0.8 years |
| 4 hours | 1,460 | about 61 days | about 1.7 years |
| 6 hours | 2,190 | about 91 days | about 2.5 years |
| 8 hours | 2,920 | about 122 days | about 3.3 years |
"Days" here means full 24-hour days. Six hours a day of screens is about three months of non-stop screen time every year.
What one hour a day really adds up to
The most useful way to use these numbers isn't to feel bad about the total. It's to see what a small change is worth.
- One hour a day is 365 hours a year, which is about 15 full days, or a little over nine 40-hour work weeks.
- Thirty minutes a day is about 182 hours a year, about seven and a half full days.
- Moving one hour from your phone to sleep takes you from, say, six hours of sleep to seven, which is the CDC's minimum for adults.
Put another way: an hour you take back from scrolling each day gives you two extra weeks a year to spend on whatever you choose, whether that's sleep, family, a skill, or simply not looking at anything.
How the Life Stats Calculator works it out
The Life Stats Calculator asks for your date of birth and lets you set your average sleep (3 to 12 hours) and daily screen time (0 to 16 hours) with two sliders. There's also an optional first name, and two questions about your mornings and your main focus right now, which only choose the light-hearted "type" at the end. The calculation runs in your browser.
For sleep and screens it does exactly what this article does: it counts the days since you were born, multiplies by 24 to get hours, takes your share of each day, and divides by 8,760 to show it in years. It shows "Hours sleeping" and "Hours on screens", each with the number of years underneath.
One honest caveat: the calculator applies today's habits to your whole life, including the years when you were a baby. So the screen-time figure answers "if I had always used screens like this", which is more than you really have. The sleep figure goes the other way and is usually lower than the truth, because you slept far more as a child. That's why it's labelled as fun, not a medical measurement.
It also shows three simple bars, all calculated from the sliders, not from any test:
- Sleep quality score: your sleep as a share of nine hours, capped at 100%.
- Screen-life balance: starts at 100% and goes down as screen time goes up, reaching 20% at 12 hours a day.
- Active hours ratio: the share of the day left after sleep and screens.
If you'd like the heartbeats, breaths and steps side of it, the heartbeats and breaths guide explains those averages.
A simple way to use your numbers
- Check your real screen time in your phone settings, and your usual bedtime and wake-up time for a week.
- Run the numbers with the calculator or the formula above.
- Pick one change worth about an hour. Charging your phone outside the bedroom, a set time to stop scrolling, or one app you limit.
- Run it again in a month with your new averages and compare the "years" figures.
It's also a fun thing to try with family or friends. Comparing "years asleep" around the dinner table usually starts a better conversation than any statistic would.
Frequently asked questions
Do we really sleep a third of our lives?
If you sleep eight hours a night, yes, because eight hours is a third of a day. At seven hours it's about 29%, and at six it's a quarter.
How do I calculate how many hours I have slept in my life?
Multiply your age in days by your average hours of sleep. A 30-year-old is about 10,950 days old (30 × 365, ignoring leap days); at 7 hours a night that's about 76,650 hours.
How many years will I spend on my phone?
Multiply your daily hours by 365 to get hours per year, then divide by 8,760 to get years. At 4 hours a day that's about 0.17 years, or two months, for every year you keep the habit.
Is the Life Stats Calculator accurate?
The arithmetic is exact, but it uses your current habits for your whole life, so treat the results as estimates for fun, not measurements.
Is my date of birth stored?
No. The calculator works it out in your browser and doesn't save or send your date of birth anywhere, and there's no account to sign up for.
Final takeaway
Your "years asleep" and "years on screens" come from the same simple sum: hours a day, divided by 24, times your age. The total isn't something to feel guilty about. The useful part is seeing that one hour a day is worth about two weeks a year, and then deciding where you'd rather spend it.