Hi Matthew
On the one occasion I have had to do these calculations (which were a nightmare), and with abatements, I set up an Excel spreadsheet with the fixed values of assets and beneficiaries’ %age shares, and then set up all the formulae to apportion the asset values between the beneficiaries and the abatements. I then set up calculations, pulling in the results of the first set of calculations, for abated total less charitable exemptions, NRB, IHT etc and then going into the Data tab used Data/What if analysis/Goal seek to do the final step. The figure in the spreadsheet which I found using goal seek, ie the variable on which other figures depended and which was not represented by a formula, was the abated total for one of the charities. From this everything else comes if you have set up the correct formulae. If you have no abatements you will be able to cut out that section of the calculations. I think you have to use goal seek as there are too many variables (hence the going round in circles) to do it otherwise. I have to say I spent hours doing it and it made my head spin.
I found some very helpful examples of the structure of the calculations in Tolley Guidance.
Good luck!
Sara Spencer
Trust and Estate