Michael,
The function you use is DateAdd. Check the help re this but basically.
Dateadd("X",Y,Z)
X is the interval => s-seconds n-minutes (!!!). .d-days,w- weekdays (!!!),ww-weeks, m-months,y-year
Y is the number of intervals (can be negative). .Z is the date you want to change.
If you just want a query to output this, just type in the the Field Dateadd("x",Y,Z) and make Z the field you want to add the interval to ..ENCLOSED in square brackets[field1].
If you want update the data use an update query
Be very careful!!. .Enter the formula as above in the "update to" field of the field you want to change.
Make sure that your Criteria is correct before running the Query.
MAx