If you're are using CRSP data, you will find that returns (RET) are already fully adjusted -- however, prices are not.
The CRSP manual has detail on how they handle splits and the series CFACPR (Cumulative Factor to Adjust Price) is easy to use as a divisor. You can double check any of your calculations knowing that RET is split-adjusted. For example, here is the case for Microsoft when they split 2 for 1 in February 2003.
PERMNO DATE TICKER PRC RET CFACPR CFACSHR
10107 20030214 MSFT 48.30 0.027878219 2 2
10107 20030218 MSFT 24.96 0.03354035 1 1
Just adjust the 2003-02-14 PRC by dividing by CFACPR to get the exact percentage return on 2003-02-18. (Usually the Shares factor CFACSHR is the same, but for some corporate actions and stock distribution schemes it is not.)
For Compustat and IBES data, the steps are sometimes even easier. In fact, most Compustat series are split adjusted and on a comparable per share basis.
For example, the Compustat PDE set shows
SMBL DATE GVKEY PRCC CUMADJ CSHOQ
MSFT 31-Jan-03 12141 23.73 2 10702
MSFT 28-Feb-03 12141 23.70 1 10702
MSFT 31-Mar-03 12141 24.21 1 10722
where PRCC is the adjusted closing price (for the month) and CUMADJ is analogous to CFACSHR. Shares Outstanding (CSHOQ) is in thousands in this set and adjusted as well. In the CRSP monthly set PRC and SHROUT are unadjusted, where the Jan 2003 PRCC of 47.46 / 2 = 23.73 (as shown in Compustat).
PERMNO DATE TICKER SHROUT PRC cfacpr
10107 20030131 MSFT 5350693 47.46 2
10107 20030228 MSFT 10701386 23.70 1
10107 20030331 MSFT 10722000 24.21 1
Note the cumulative adjustments are needed to restate prices and shares into comparable terms, but for returns, the daily noncumulative adjustment factor is usually enough.
The most important things to find out is whether the series you are using is split-adjusted or not and whether the dataset has a cumulative adjustment factor that you can use. The database manual and other documentation on WRDS should answer these questions.