Whether you’re tracking the decay of radioactive isotopes, estimating the depletion of a drug in the bloodstream, or forecasting depreciation of assets, understanding half-life is crucial. Our Half-Life Calculator provides an easy, fast, and accurate way to determine how much of a substance or value remains after a given period of time — without any manual math.
In this guide, we’ll walk you through how the tool works, step-by-step instructions for use, real-world examples, and answers to common questions.
Half-Life Calculator
What Is the Half-Life Calculator?
The Half-Life Calculator is a time-decay calculation tool that determines:
- Remaining Amount — how much is left after a certain time
- Percentage Remaining — the proportion of the original amount still present
- Amount Decayed — how much has diminished over the period
By applying the standard half-life formula: Remaining Amount=Initial Amount×0.5(Time ElapsedHalf-Life)\text{Remaining Amount} = \text{Initial Amount} \times 0.5^{\left(\frac{\text{Time Elapsed}}{\text{Half-Life}}\right)}Remaining Amount=Initial Amount×0.5(Half-LifeTime Elapsed)
…it removes the need for manual calculations, letting you focus on interpreting results.
📋 How to Use the Half-Life Calculator (Step-by-Step)
- Enter the Initial Amount
- Input the starting value (e.g., grams, dollars, milligrams).
- The calculator accepts decimal values.
- Enter the Half-Life (in years)
- Specify the known half-life of the material or value.
- For drugs or other substances with shorter half-lives, still enter the equivalent in years (you can convert days or hours to years beforehand).
- Enter the Elapsed Time (in years)
- Input how long the substance or value has been decaying.
- Click "Calculate"
- The results will display:
- Remaining Amount
- Percentage Remaining
- Amount Decayed
- The results will display:
- Click "Reset" (optional)
- Clear all fields and start a new calculation.
📊 Practical Examples
Example 1: Radioactive Decay
A 10 g sample of Carbon-14 (half-life ~5,730 years) has been sitting for 11,460 years.
- Initial Amount: 10 g
- Half-Life: 5,730 years
- Elapsed Time: 11,460 years
Result:
- Remaining Amount: 2.50 g
- Percentage Remaining: 25%
- Amount Decayed: 7.50 g
This means 75% of the Carbon-14 has decayed after two half-life periods.
Example 2: Pharmaceutical Elimination
A patient receives a 200 mg dose of a medication with a half-life of 6 hours. After 18 hours:
- Convert time to years: 18 hours≈0.00205 years18\ \text{hours} \approx 0.00205\ \text{years}18 hours≈0.00205 years
- Half-Life: 0.000684 years0.000684\ \text{years}0.000684 years (6 hours)
- Elapsed Time: 0.00205 years
Result:
- Remaining Amount: 25 mg
- Percentage Remaining: 12.5%
- Amount Decayed: 175 mg
Example 3: Asset Depreciation
A $50,000 machine loses half its value every 4 years. After 10 years:
- Initial Amount: $50,000
- Half-Life: 4 years
- Elapsed Time: 10 years
Result:
- Remaining Amount: $8,838.83
- Percentage Remaining: 17.68%
- Amount Decayed: $41,161.17
💡 When to Use the Half-Life Calculator
- Nuclear physics — isotope decay measurement
- Pharmacology — drug elimination tracking
- Environmental science — pollutant degradation
- Finance — depreciation models
- Chemistry — unstable compound breakdown
- Food science — shelf-life estimation
❓ Frequently Asked Questions (FAQs)
1. What is half-life?
Half-life is the time required for a quantity to reduce to half its initial value due to decay or depletion.
2. Can this calculator handle units other than years?
Yes. Convert your time and half-life to years before entering them.
3. Does the calculator work for growth instead of decay?
No. This tool is specifically for decay processes.
4. Can I use it for drug dosage planning?
Yes, but always confirm results with a medical professional.
5. Is it accurate for very short half-lives?
Yes, as long as you use precise time conversions.
6. What happens if I enter zero or negative numbers?
The calculator will prompt you to enter valid values.
7. Can I use it for financial depreciation?
Yes, as long as the depreciation follows a half-life pattern.
8. Does it store my input data?
No. All calculations are done locally in your browser.
9. How precise are the results?
Results are shown to two decimal places by default.
10. Can I calculate backwards (find time from remaining amount)?
Not with this tool — it calculates remaining amount only.
11. Does the initial amount have to be money?
No. It can be mass, concentration, population, etc.
12. Can I calculate for more than one substance at a time?
You’d need to run separate calculations for each.
13. Is the half-life always constant?
Yes, for ideal decay processes. In reality, some variables may cause variation.
14. Can I print the results?
Yes — you can print your browser page or take a screenshot.
15. Is there a limit to the number of calculations?
No. You can calculate as many times as you like.
16. Can I use decimals in my input?
Yes, the calculator supports decimals for more accurate results.
17. Is this tool mobile-friendly?
Yes, it works on smartphones, tablets, and desktops.
18. How is percentage remaining calculated?
It’s (Remaining Amount/Initial Amount)×100(\text{Remaining Amount} / \text{Initial Amount}) \times 100(Remaining Amount/Initial Amount)×100.
19. Can I use it for biological decay (e.g., bacteria death)?
Yes, if the decay follows a predictable half-life.
20. Does it work offline?
Yes, as long as the calculator page is already loaded.