Radiocarbon Date Calibrator

Radiocarbon dating measures how much carbon-14 remains in an organic sample relative to the ratio living tissue holds while exchanging carbon with the atmosphere. Carbon-14's most precisely measured physical half-life is 5,730 years (the Cambridge value), but by the international reporting convention set out in Stuiver and Polach's 1977 paper "Discussion Reporting of 14C Data" (published in the journal Radiocarbon), every reported "radiocarbon age" — including the age this calculator takes as input, and the scale calibration curves like IntCal20 are actually indexed against — is calculated using the older, less accurate Libby half-life of 5,568 years instead, deliberately preserved for continuity with decades of previously published dates. This calculator's remaining-carbon-14 figure follows that same convention, so the fraction remaining shrinks predictably with age at the Libby rate — this calculator reports that remaining fraction alongside the raw radiocarbon age. A raw radiocarbon age (measured in years BP, "before present" meaning before 1950) is not the same as a calendar age, because the atmospheric ¹⁴C/¹²C ratio has not been constant through history — it has wobbled with solar activity, the carbon cycle, and the geomagnetic field. Labs correct for this using a calibration curve such as IntCal20, built from tree rings, corals, and other dated proxies.

This calculator applies a simplified piecewise-linear approximation of that relationship rather than the real IntCal20 dataset, so treat the calendar age and calendar year as an order-of-magnitude estimate for planning a sample's likely period, not a publication-grade calibrated date. For marine or freshwater samples, a reservoir correction (ΔR) is subtracted first, since organisms in those environments incorporate old, depleted carbon and read artificially old. The 1-sigma and 2-sigma ranges widen the reported laboratory uncertainty to reflect the added imprecision of calibration itself. For real archaeological or geological work, run the reported radiocarbon age and uncertainty through OxCal or CALIB against the actual IntCal20/Marine20 curves.