You don't have enough points to infer any kind of regression. I mean, if you look at:
data = [0.25 0.256
0.24 0.24
0.224 0.24
0.26 0.27
0.24 0.26];
scatter(data(:, 1), data(:, 2));
there's no pattern to your data.
If you want to do a linear regression anyway:
polystartend = polyfit(data(:,1), data(:, 2), 1); %linear regression
todaystart = 21;
todayend = polyval(polystartend, todaystart)
gives
todayend = 0.22688
