Advanced Uranium Lead Dating Calculator

Calculator Inputs

206Pb / 238U Ratio

Primary ratio for the 238U decay system.

207Pb / 235U Ratio

Secondary ratio for the 235U decay system.

207Pb / 206Pb Ratio

Optional radiogenic ratio for older samples.

238U / 235U Ratio

Common natural value is around 137.818.

Ratio Uncertainty (%)

Used to estimate age uncertainty bands.

Sample Mass (mg)

Supports concentration based screening outputs.

Uranium Concentration (ppm)

Measured total uranium in the selected aliquot.

Lead Concentration (ppm)

Measured total lead before common correction.

Common Lead Fraction

Enter a value from 0 to below 1.

Formula Used

206Pb / 238U age:
t = ln(1 + 206Pb/238U) / λ238

207Pb / 235U age:
t = ln(1 + 207Pb/235U) / λ235

207Pb / 206Pb age:
207Pb/206Pb = [(e^(λ235t) − 1) / (e^(λ238t) − 1)] / (238U/235U)

This page uses λ238 = 1.55125 × 10^-10 year^-1 and λ235 = 9.8485 × 10^-10 year^-1. Ages are reported in millions of years. Concordance compares the two independent ages, while discordance highlights possible isotopic disturbance, lead loss, inheritance, or analytical mismatch.

How to Use This Calculator

Enter measured isotopic ratios from your sample analysis.
Keep the natural 238U/235U ratio unless your method requires another value.
Add uncertainty and concentration values for broader interpretation outputs.
Enter an estimated common lead fraction for corrected radiogenic screening.
Press the calculate button to show results above the form.
Review weighted age, concordance, discordance, and mass based diagnostics together.
Use the CSV or PDF buttons to save the output.
Compare ages with petrography and laboratory quality controls before final interpretation.

Sample	206Pb/238U	207Pb/235U	207Pb/206Pb	U ppm	Pb ppm	Common Pb
Zircon A	0.1850	1.8200	0.0725	850	125	0.020
Zircon B	0.2420	2.7600	0.0832	910	143	0.018
Monazite C	0.5120	6.3400	0.1185	1320	266	0.026
Baddeleyite D	0.0890	0.8150	0.0601	640	79	0.015

Frequently Asked Questions

1. What does uranium lead dating measure?

It estimates geological age from radioactive uranium decaying into lead isotopes. Separate decay chains provide independent ages that can be compared for reliability and disturbance screening.

2. Why are there two main uranium lead ages?

Uranium has two important isotopes, 238U and 235U. Each decays at a different rate and produces a separate age estimate using different daughter lead isotopes.

3. What does concordance mean here?

Concordance measures how closely the 206Pb/238U and 207Pb/235U ages agree. High concordance usually supports stronger confidence in the sample’s isotopic system.

4. What can cause discordance?

Lead loss, metamorphism, inheritance, common lead contamination, altered minerals, or analytical problems can shift isotopic ratios and make the two ages disagree.

5. Is the 207Pb/206Pb age always required?

No. It is especially useful for older samples and concordia style interpretation. The calculator accepts it as an additional diagnostic rather than a strict requirement.

6. What is common lead fraction?

It represents non-radiogenic lead already present in the mineral or system. Correcting for it helps isolate radiogenic lead formed by uranium decay.

7. Are the outputs suitable for publication?

This calculator is best for screening, teaching, and fast checks. Published ages should still rely on calibrated laboratory workflows, standards, corrections, and full uncertainty treatment.

8. Why include uranium and lead concentrations?

Those fields add context for sample quality and simple mass calculations. They help users connect isotopic ages with concentration based screening information.