Determining Date Range from Pay Date Information

Question

I have a table of employees with different pay dates because they are college interns and they leave at different dates, so their most recent pay date will be different. I have created a query to find the most recent pay date.  The pay periods are bi-weekly.
I have a table called tblPayPeriods with all of the pay dates. I have created a query that pulls the most current pay date for each intern and I want to match that pay date to the pay date of the Pay Periods table and increment back twenty pay periods. 
Once I have determined the oldest pay date I want to use that range for a calculation for average hours ultimately.  I can handle the average hours part but I'm having trouble with the pay dates part of this. Any suggestions would be appreciated. 
Thanks!
Here is the SQL statement to find the most current pay date for each intern:
SELECT tblMeasurementPeriod.EENum, Max(tblMeasurementPeriod.[Pay Date]) AS [MaxOfPay Date]
FROM tblEmployees INNER JOIN tblMeasurementPeriod ON tblEmployees.[EE Num] = tblMeasurementPeriod.EENum
WHERE (((tblEmployees.[Measurement Period])="initial"))
GROUP BY tblMeasurementPeriod.EENum;
Here is the SQL statement using the query joined to the pay date table:
SELECT qryFindLatestPayDateforINITIAL.EENum, qryFindLatestPayDateforINITIAL.[MaxOfPay Date], tblPayDate.[Pay Date]
FROM qryFindLatestPayDateforINITIAL INNER JOIN tblPayDate ON qryFindLatestPayDateforINITIAL.[MaxOfPay Date] = tblPayDate.[Pay Date];
Alicia Hunsberger

Answer 1

You have the Intern Last Pay Date (LPD)
You want to match that LPD to the pay date of the Pay Periods table...
** so the first question is - are you able to? what is the obstacle on this?
and increment back twenty pay periods
** is there a fixed math you can rely on, such as subtract 180 days?...will that work to determine the pay date 20 periods previously?  it would be great if the pay periods had a sequential integer in their record - - - that would make it easy....