Science calculator
Half-Life Calculator
Calculate radioactive decay remaining.
About the half-life calculator
The half-life calculator computes remaining radioactive material after a given time.
How to use this calculator
- 1
Enter initial amount
Enter the starting amount.
- 2
Enter half-life
Enter the half-life in the same time units as elapsed time.
- 3
Enter elapsed time
Enter how much time has passed.
How the calculation works
N = N₀ × (1/2)^(t/t½).
Example: 100g, t½=5yr, t=15yr: 12.5g remaining.
Understanding scientific constants
Key constants used: g = 9.81 m/s² (Earth gravity), c = 299,792,458 m/s (speed of light), G = 6.674×10⁻¹¹ N·m²/kg² (gravitational constant), h = 6.626×10⁻³⁴ J·s (Planck's constant), R = 8.314 J/(mol·K) (ideal gas constant). Results assume ideal conditions — real-world measurements may vary.
Ideal vs. real-world conditions
Most physics calculators assume ideal conditions: no air resistance, perfect vacuums, uniform gravity. Real-world results will differ due to friction, air resistance, temperature variations, and measurement uncertainty. Use these tools for learning and estimation, not precision engineering.
Important limitations
This tool provides a mathematical estimate based only on the values entered. It does not account for regulations, taxes, lender fees, market conditions, or individual circumstances. Results are for planning purposes only — consult a qualified professional for regulated, medical, financial, or construction decisions.
Frequently asked questions about half-life calculator
How accurate is the half-life calculator?+
The calculation follows the displayed formula and retains full numeric precision before formatting the result.
Can I use the result professionally?+
Use it as a planning estimate. Confirm regulated, medical, financial, or construction decisions with a qualified professional.