The simplest model is one saying that serum estradiol is proportional to serum testosterone. The normal constant of proportionality is in the range of 0.3 to 0.6%. Various things can change the constant of proportionality. For me, using hCG pushes the proportionality from about 0.5% to 0.7%. A somewhat more sophisticated model is described in
this work.
In all cases, the combined data exhibited curvilinear relationships that were well described by a rectangular hyperbolae, Y = A X/ (B + X), consistent with a saturable conversion of testosterone to metabolite governed by Michaelis-Menten kinetics ...
If you are motivated then you can use your data to find the best fit for the A and B constants. I've done this with pretty decent results.
A further incremental improvement is to base the calculation for total estradiol on the amount of free testosterone, which is what actually aromatizes.
Of course to make use of any of this you still need to describe your particular pharmacokinetics for testosterone cypionate. If you have to measure your serum testosterone at all of the time points of interest then you might as well just measure estradiol too.
If you just want to get a general sense of how serum levels might change over time then plug your dose data into
SteroidPlotter - Graph your cycle