Screen Time Calculator
Calculate total screen time per year and over a lifetime from daily hours on phones, TV, and computers.
Returns hours per year and lifetime total by age 70.
This calculator estimates your daily screen exposure hours, the associated blue light load, and how your usage compares to research-based thresholds for eye strain, sleep disruption, and cognitive fatigue.
The primary formula combines all device usage into a weighted daily total:
Weighted Screen Hours = Σ (Device Hours × Blue Light Weight Factor)
Blue Light Weight Factors (approximate):
- Smartphone (close distance): 1.5×
- Tablet: 1.3×
- Computer monitor: 1.0×
- Television (3+ meters away): 0.4×
Eye Strain Risk Score is then calculated as:
Risk Score = Weighted Hours × Distance Penalty × Blink Reduction Factor
Where close screens (<50 cm) carry a 1.4× distance penalty and typical blink rate drops from 15 to ~5 blinks/minute during screen use (a 3× blink reduction factor).
Worked Example: A user works 8 hours at a monitor, uses a phone 3 hours, and watches TV 2 hours:
- Monitor: 8 × 1.0 = 8.0
- Phone: 3 × 1.5 = 4.5
- TV: 2 × 0.4 = 0.8
- Weighted total = 13.3 hours
The 20-20-20 Rule recommends: every 20 minutes, look at something 20 feet away for 20 seconds. This resets the ciliary muscle and reduces strain by an estimated 40%.
Reference Limits: AAP recommends ≤2 hours/day for adults (leisure); WHO links >4 hours/day sedentary screen time to elevated depression risk. Average US adult now exceeds 11 hours/day of screen exposure across all devices.