https://www.researchgate.net/post/LC50_value_calculations

https://www.researchgate.net/post/Can_anyone_give_me_details_for_the_calculation_of_LC50_LD50_IC50_of_drugs_against_cultured_cancerous_cells

please look for probit analysis using spss 

Or if you would use R, than drc library is amazing.

Dear Sir,

try and see my answer in this site:

https://www.researchgate.net/post/Dear_all_Anybody_have_any_idia_about_how_to_calculate_IC50_and_p_value

https://www.researchgate.net/post/Dear_all_Anybody_have_any_idia_about_how_to_calculate_IC50_and_p_value

the concentration of an agent which kills the 50% of the the target, that could be bacteria, viruses or if you are measuring the growth, the concentration which inhibit the growth of 50% of the organisms...

It is also called Lethal dose50

Cheers