Multiple variants of the ΛCDM model are used with some differences in parameters.<ref name=PDG-2024/>{{rp|loc=25.1}} One such set is outlined in the table below.
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The [[Planck (spacecraft)|Planck]] collaboration version of the ΛCDM model is based on six [[parameter]]s: physical baryon density parameter; physical dark matter density parameter; thescalar agespectral ofindex; thetwo universe;parameters scalarrelated spectral index;to curvature fluctuation amplitude; and reionizationthe opticalprobability depth.<ref>{{citethat journal|title=Thephotons darkfrom sidethe ofearly theuniverse cosmology:will darkbe matterscattered andonce darkon energy|author=Spergel,route (called reionization Doptical depth).<ref N.|journalname=Science|volume=347|issue=6226|year=2015|doi=10.1126/science.aaa0980|pmid=25745164|pages=1100–1102|bibcode=2015Sci...347.1100S|doi"Planck-access=free}}<2013"/ref> Six is the smallest number of parameters needed to give an acceptable fit to the observations; other possible parameters are fixed at "natural" values, e.g. total density parameter = 1.00, dark energy equation of state = −1. (See below for extended models that allow these to vary.)
The values of these six parameters are mostly not predicted by theory, except that most versions of [[cosmic inflation]] predict the scalar spectral index should be slightly smaller than 1, consistent with the estimated value 0.96. The parameter values, and uncertainties, are estimated using large computer searches to locate the region of parameter space providing an acceptable match to cosmological observations. From these six parameters, the other model values, such as the [[Hubble's law|Hubble constant]] and the [[dark energy]] density, can be readily calculated.
Parameter values listed in the table are from the ''Planck'' Collaboration Cosmological parameters 68% confidence limits for the base ΛCDM model from ''Planck'' CMB power spectra, in combination with lensing reconstruction and external data (BAO + JLA + H<sub>0</sub>).<ref name="Planck 2015">{{cite journal | author = Planck Collaboration | title = Planck 2015 results. XIII. Cosmological parameters | arxiv = 1502.01589 | doi=10.1051/0004-6361/201525830 | volume=594 | issue = 13 | journal=Astronomy & Astrophysics | page=A13 | bibcode=2016A&A...594A..13P| year = 2016 | s2cid = 119262962 }}</ref> See also [[Planck (spacecraft)]].
