  A new semi-empirical formula for calculations of $\alpha$~decay halflives is
presented. It was derived from Royer relationship by introducing new parameters
which are fixed by fit to a set of experimental data. We are using three sets:
set A with 130 e-e (even-even), 119 e-o (even-odd), 109 o-e, and 96 o-o, set B
with 188 e-e, 147 e-o, 131 o-e, and 114 o-o, and set C with 136 e-e, 84 e-o, 76
o-e, and 48 o-o alpha emitters. A comparison of results obtained with the new
formula and the following well known relationships: semFIS (semiempirical based
on fission theory), ASAF (analytical superAsymmetric fission) model, and UNIV
(universal formula) is made in terms of rms standard deviation. We also
introduced a weighted mean value of this quantity, allowing to compare the
global properties of a given model. For the set B the order of the four models
is the following: semFIS, UNIV, newF, and ASAF. Nevertheless for even-even
alpha emitters UNIV gives the 2nd best result after semFIS, and for odd-even
parents the 2nd is newF. Despite its simplicity in comparison with semFIS the
new formula, presented in this article, behaves quite well, competing with the
others well known relationships.
