In crude death rate the population is taken as on -
A rate comprises the following elements →

i) Numerator
ii) Denominator
iii) Time specification       
iv) Multiplier
Numerator → Refers to the number of times an event (e.g. sickness, birth, death) has occurred in a population, during a specified time period. Numerator is a component of the denominator in calculating a rate, but not in a ratio.
Denominator → Denominator may be :-
i) Related to population
Mid year population → population estimated on first of July of an year
Population at risk
Person - time
Person distance
ii) Related to total events
 As in case fatality rate, denominator is total number of cases rather than total population.
1st March
1st July
1st April
15th August