We discuss the uncertainties in constraining low-energy constants of chiral effective field theory from 3 H β decay. The half-life is very precisely known, so that the Gamow-Teller matrix element has been used to fit the coupling cD of the axial-vector current to a short-range two-nucleon pair. Because the same coupling also describes the leading one-pion-exchange three-nucleon force, this in principle provides a very constraining fit, uncorrelated with the 3 H binding energy fit used to constrain another low-energy coupling in three-nucleon forces. However, so far such 3 H half-life fits have only been performed at a fixed cutoff value. We show that the cutoff dependence due to the regulators in the axial-vector two-body current can significantly affect the Gamow-Teller matrix elements and consequently also the extracted values for the cD coupling constant. The degree of the cutoff dependence is correlated with the softness of the employed NN interaction. As a result, present three-nucleon forces based on a fit to 3 H β decay underestimate the uncertainty in cD. We explore a range of cD values that is compatible within cutoff variation with the experimental 3 H half-life and estimate the resulting uncertainties for many-body systems by performing calculations of symmetric nuclear matter. Introduction. The development of new and improved nuclear forces within chiral effective field theory (EFT) is currently a very active field of research [1][2][3][4]. In contrast to phenomenological approaches, chiral EFT provides a framework that allows to systematically derive improvable expansions for nucleon-nucleon (NN) and many-body forces as well as electroweak current operators at low energies [5][6][7][8]. Within Weinberg's power counting scheme [9] the contributions to NN forces have been worked out up to fifth order in the chiral expansion [3, 10], whereas three-nucleon (3N) and four-nucleon forces have been developed up to fourth order [11][12][13][14]. Similarly nuclear currents have been derived up to fourth order for axial-vector [15,16] and vector currents [17][18][19][20][21].The contributions to nuclear forces and currents generally depend on low-energy couplings (LECs) that capture the short-distance physics that is not resolved explicitly within the EFT. Therefore, to determine the LECs, fits to data are needed. Up to second (next-to-leading) order there are no contributions from many-body interactions or currents, and the LECs in the NN forces are usually obtained by fits to pion-nucleon and nucleon-nucleon scattering data. At third (next-to-next-to leading) order, N 2 LO, two additional LECs, c D and c E , enter in 3N forces and two-body (2b) currents. While c D enters in both the NN-contact-one-pion exchange 3N force and the