  We derive new constraints on the neutron lifetime based on the recent Planck
2015 observations of temperature and polarization anisotropies of the CMB.
Under the assumption of standard Big Bang Nucleosynthesis, we show that Planck
data constrains the neutron lifetime to $\tau_n=(907 \pm 69) \, [\text{s}]$ at
$68 \%$ c.l.. Moreover, by including the direct measurements of primordial
Helium abundance of Aver et al. (2015) and Izotov et al. (2014), we show that
cosmological data provide the stringent constraints $\tau_n=(875 \pm 19) \,
[\text{s}]$ and $\tau_n=(921 \pm 11) \, [\text{s}]$ respectively. The latter
appears to be in tension with neutron lifetime value quoted by the Particle
Data Group ($\tau_n=(880.3 \pm 1.1) \, [\text{s}]$). Future CMB surveys as
COrE+, in combination with a weak lensing survey as EUCLID, could constrain the
neutron lifetime up to a $\sim 6 \, [\text{s}]$ precision.
