Example preset
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Inputs
Results
| Half-life number n (t/T) | — |
|---|---|
| Remaining amount N | — |
| Survival rate r (N/N0) | — |
|---|---|
| Survival rate (%) | — |
Era conversion (optional)
| Estimated age (counted backwards from base year) | — |
|---|---|
| Estimated BP (1950 standard) | — |
*Year/BP is an uncalibrated approximate display (for learning purposes).
Details (decay constant λ / average life τ)
| Decay constant λ | — |
|---|---|
| Average lifespan τ | — |
| year definition | — |
Graph (time → survival rate)
The graph shows the decay of survival rate over time. The linear display shows the survival rate %, and the logarithmic display shows the survival rate r.
Enter values to draw the survival-rate curve over time.
| time | Survival rate r | Survival rate (%) |
|---|---|---|
| Displays representative points after displaying the graph. | ||
Calculation procedure
Enter values to show the calculation steps.
Assumptions & limits
- This is an approximation based on an idealized exponential decay model (single decay).
- In the practice of radiometric dating, additional analyzes such as establishment of a closed system, initial conditions, isotopic ratios, and corrections are required.
- The year (yr) is fixed as the Julian year (365.25 days).
- The input values are calculated within the browser and can be reproduced in the shared URL.
Study notes (half-life and dating)
This tool uses the simple exponential-decay model N(t)=N0·exp(-λt) (λ=ln2/T). It is suitable for checking formulas and estimating orders of magnitude.
Examples of main nuclides and uses
| nuclide | half-life | Main usage examples |
|---|---|---|
| Carbon-14 (C-14) | 5,730 years | Archeology and paleoenvironmental samples (tens of thousands of years scale) |
| Potassium-40 (K-40) | 1.248 billion years | Geological age estimation of volcanic rocks, etc. |
| Uranium-238 (U-238) | 4.468 billion years | Earth history scale chronological discussion |
| Iodine 131 (I-131) | 8 days | Confirmation of decay of short-lived nuclides |
Differences from practice (important)
- Radiometric dating verifies the establishment of a closed system, initial conditions, contamination, equipment correction, etc.
- The C-14 era requires a calibration curve, which may not match the simple equation.
- The Western calendar/BP conversion in this calculator is an approximate learning display and cannot be used as a reported value.
FAQ
Is this age the same as the actual radiometric dating?
No. This calculator uses an ideal exponential-decay model. Real radiometric dating also needs checks for closed-system behavior, initial conditions, isotope ratios, and corrections.
What is the definition of "year"?
This tool calculates Julian year (365.25 days) as one year.
What are the units of initial amount N0 and remaining amount N?
Please enter in the same unit (g, mol, number, etc.). The ratio r=N/N0 is dimensionless.
How is the BP (Before Present) display calculated?
It shows uncalibrated BP by converting the estimated event year to a 1950 baseline. Research use requires calibration curves and measurement checks.
What should I check first before trusting this age estimate?
Confirm that the half-life, initial amount, and remaining amount all describe the same nuclide and use the same units. A mismatch there is the fastest way to produce a meaningless age.
How to use this dating calculator
This page is for classroom and lab-style back calculations from half-life data. Use it when you want to translate a remaining fraction into elapsed time, not when you need a calibrated research workflow.
Recommended path
- Choose the known input pattern first: half-life plus ratio, half-life plus remaining amount, or half-life plus elapsed time.
- Keep the same unit for initial amount and remaining amount so the ratio stays meaningful.
- Use the optional BP/year conversion only as an educational reference, not as a calibrated dating result.
Related tools
- Physics tools and calculators | CalcBEBrowse additional physics calculators when you need a broader reference around radioactive decay or half-life concepts.
- Earth science tools and calculators | CalcBEOpen related earth-science pages when you want classroom context around age, strata, and geological interpretation.
- Earthquake b-value calculator (Gutenberg-Richter) | CalcBEUse a nearby earth-science calculation when you are moving from dating concepts to earthquake-catalog interpretation.
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