Realize that it may never be possible to pinpoint precisely when a person was born. In some locations and time periods, there simply may not be records providing a specific date of birth--the year (or even an estimate of it) may be as precise as you can get. There may be no record of a death, just the last record where a person is referenced as being alive.
The important thing is to establish relationships as best you can. It might not be pivotal whether a person was born in March or April of 1838.