You could try ProtParam Tool from the SIB ExPASy webserver, It will predict half life starting from your primary amino acids sequence.
http://web.expasy.org/protparam/
The parameters computed by ProtParam include the molecular weight, theoretical pI, amino acid composition, atomic composition, extinction coefficient, estimated half-life, instability index, aliphatic index and grand average of hydropathicity (GRAVY).