Calling all actuari...
 

  You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more

[Closed] Calling all actuaries/accountants/maths boffs, I need a formula...

6 Posts
4 Users
0 Reactions
43 Views
 IHN
Posts: 19694
Full Member
Topic starter
 

Somethng to flex your brains with (or look up in a book, as I bet it's a fairly standard thing) of a Friday morning.

I'd like a formula that shows the initial investment required to allow for a given
- yearly income
- number of years that the income is to be taken
- yearly rate of increase on the income
- yearly return on the remaing investment

You know, like how much would be needed up front to take £20k a year, rising at 5% a year, for 25 years with an average investment return per year of 7%.

It feels like a fairly standard pensions/annuity type thing, but I can't find anything on the interweb...


 
Posted : 12/12/2014 10:21 am
Posts: 36
Free Member
 

Cant think of the formula as uyou cant use PMT as there's no inflation argument.

Id just build a cashflow and solve with a goalseek, but then thats the last refuge of an Excel blagger like me 🙂

I can even do it for you if you like...


 
Posted : 12/12/2014 10:26 am
Posts: 0
Free Member
 

You should add in inflation to the requirement


 
Posted : 12/12/2014 10:27 am
 IHN
Posts: 19694
Full Member
Topic starter
 

[i]Id just build a cashflow and solve with a goalseek[/i]

I love it when you talk dirty.


 
Posted : 12/12/2014 10:28 am
 IHN
Posts: 19694
Full Member
Topic starter
 

[i]You should add in inflation to the requirement

[/i]

Why's that then? I've got the income rising (to take into account inflation)


 
Posted : 12/12/2014 10:29 am
Posts: 0
Free Member
 

That's fine if you want to keep it simple. It didn't sound like the rate of rise percentage was to cover inflation but if it is, as you say, there's no need.


 
Posted : 12/12/2014 10:30 am
Posts: 0
Free Member
 

Its easy enough to do in excel

A column showing income rising at 5% per year, a column showing capital rising at 7% per year with the annual income subtracted, plug a capital figure into the first cell and tweak it until you're left with £0 capital at year 25.

You can set it up to change any of the variables to see what comes out.

In your example you would need £364,182.45 initial investment.

Edit: missed year 25 income off the calculation so capital would need to be £376,066.89

But that's in very simple annual terms.


 
Posted : 12/12/2014 10:56 am

6 DAYS LEFT
We are currently at 95% of our target!