This program uses Cohen's d as the effect size as recommended by Dunlop, W. P., Cortina, J. M., Vaslow, J. B., & Burke, M. J. (1996) for a paired t-test.

Alpha is the (two-tailed) type I error, mdiff is the difference in group means, sd is the average group standard deviation with (common group) sample size inputted as n. The program then outputs the power.

Reference:

Dunlop, W. P., Cortina, J. M., Vaslow, J. B., & Burke, M. J. (1996). Meta-analysis of experiments with matched groups or repeated measures designs. Psychological Methods, 1, 170-177.

[COPY AND PASTE THE SYNTAX BELOW INTO A SPSS SYNTAX WINDOW AND RUN; ADJUST DATA INPUT VALUES AS REQUIRED]

DATA LIST free
/alpha mdiff sd n rho. 
BEGIN DATA. 
.05 2.0 4.0 40  0.0
.05 2.0 4.0 40  0.3
END DATA. 

matrix.
get m /variables=alpha mdiff sd n rho  /missing=omit.
compute alpha=make(1,1,0).
compute mdiff=make(1,1,0).
compute sd=make(1,1,0).
compute n=make(1,1,0).
compute rho=make(1,1,0).
compute alpha=m(:,1).
compute mdiff=m(:,2).
compute sd=m(:,3).
compute n=m(:,4).  
compute rho=m(:,5).
end matrix.
COMPUTE power = 1 - NCDF.T(IDF.T(1-alpha/2,n+n-2),n+n-2,(mdiff)/SQRT((2*sd*sd/n)*(1-rho))).
exe.
formats n (f7.0) rho (f7.2) alpha (f5.2) mdiff (f5.2) sd (f5.2) power (f5.2).
variable labels n 'Sample Size 1' /rho 'Correlation' /alpha 'Alpha' /mdiff 'Mean Difference' /sd 'SD' /power 'Power'.
report format=list automatic align(center)
  /variables=n rho alpha mdiff sd power 
  /title "Paired t-test power for given sample size" .