This calculator is referred to in this article published in the GBI yearbook.
It is a macro free 2016 Excel spreadsheet. The calculator is pre-populated with the example portfolios given in the article. But any cells shaded green are free-format so you can put in your own figures and create your own scenarios. (If you need to reset the figures just download the spreadsheet again.)
We also host an online calculator to illustrate the detail of SEIS & EIS tax reliefs on an individual investments and have produced a simple one-page summary of SEIS & EIS reliefs and criteria. Feel free to use them with your colleagues & clients and let us know if they are useful!