Again the figures are very conservative and they are FEES only excluding school trips uniforms food etc based off ACTUAL paid fees simply projected forward. I simply fail to see how this is not a reasonable assumption.

Show me your alternate calculations?

As frugalnacho said, this isn't a matter of questioning your calculations, but of your inputs. It's the inputs that I (and others) are having a hard time understanding. People here are just trying to help and understand.

Here's the inputs that I either don't agree with, or cannot wrap my head around.

1) you have included 5 years of university per child, and private school from age 4 to age 23.

2) Your estimate for University, which you say is real-adjusted, goes up to £75k ($112k USD) for a single year. You stated you are using a conservative estimate of a 5% annual increase over inflation. Back-calculating, this indicates in input of £28,500 per year for (all?) expenses per year of university. Then you calculations assume this will increase almost 3x in real-adjusted terms over hte next two decades.

3) the only option you are considering is keeping your children in a £15k (today's money) private school (includes all expenses) from age 4 through age 18.

Here are the concerns I have with your inputs:

1a) why are you assuming 5 years of university, and why are you incurring all costs? UK universities typically offer undergraduate degrees in 3 years, and most masters programs are a single year. Are you budgeting for undergraduate and two masters degrees?

2a) I believe your current estimate of what one year of university cost is way too high. Currently, one year at many of the UK's top universities - including rent, books, tuition etc comes out to about £15k. Your inputs are assuming costs today are almost twice that.

2b) I think your assumption that costs will show a real-increase of 5%/year for the next decade are absurd. At that level of increase the overwhelming majority of Brits could not afford to attend.

3a) there are many other options besides sending your child to the most expensive private schools available for 15 consecutive years.