The part of the sentence "based on the average monthly" is correct and usable in written English.
You can use this phrase when you need to describe something that is calculated from an average of monthly data or measurements. For example: "The estimates for the project are based on the average monthly revenues for the past three months."
The value was based on the average monthly income in Finland of €2807 for women and €3422 for men (Statistics Finland 2011).
The home-makers' earning were estimated based on the average monthly salaries of the persons doing various jobs in the house, i.e. housekeeping, cooking and babysitting.
The period was calculated in working days and then multiplied by average day-income including social security contributions based on the average monthly market income in the county [ 19] (Table 3).
The first method is based on the average annual monthly values in which the size of photovoltaic and wind generators was determined from the average monthly contribution of each component.
The strata were based on the mean monthly attendance.
Counts of needlestick injuries for the first three months of 2006 were imputed based on the average number of needlestick injuries reported monthly for this year of data in order to examine trends over the period 2006 2011.
Analysis of variance with repeated measures was used to compare monthly mean (based on the average per house in each site) temperatures throughout the entire study period.
Under the new contract, a typical pilot's monthly pay would immediately increase more than $1,500, based on the average pilot salary of about $158,500 last year.
The correspondence between U.S. EPA annual averages and annual averages based on the monthly averages was very strong (r = 0.996).
Based on the monthly average rainfall intensity, the study area was divided into two main zones of natural soil humidity.
These datasets are based on the monthly average and are available from 1979 to the present day.
