How to plan for Retirement Fund?

Generally, we all start to think how much do we need for retirement. Retirement fund is also called as Annuity or Pension Fund from which we can withdraw a fixed amount. 

I wanted to calculate the retirement fund in the following ways.

1. Regular Annuity - Fixed withdrawal for limited time with no cash left behind
2. Inflation Adjusted Annuity - Withdrawal adjusted to inflation for limited time with no cash left behind
3. Perpetuity or Infinite Annuity.(Inflation not adjusted)

Regular Annuity

1. Monthly Expense NOW
Our monthly expense is 20,000. This is without school fees, parties, eating out, etc.

My husband is ~30 now and he might work till 50. So, after that we would need retirement fund for 20 years. (Everything is in God's hands!)

2. Monthly Expense in FUTURE


Years : 20 
Inflation : 15.
Amount needed after 20 years : 20000*(1+15/100)^20 (Compound Interest formula : P[1+R/100)^N])

Amount needed : 3,27,330.74


3. Annuity calculation

Number of Years after Retirement : 20
Rate of Interest : 8%
Annuity Principal Amount required: 3,93,94,687.68 ( Annuity = PV(rate,nper,pmt,,1))

4. Savings plan (SIP) for Retirement Fund

So, our family should catch up with 3,93,94,687.68 before my husband turns 50. 

This could be calculated using PMT in Excel.
SIP Monthly = 66,881.70. [PMT(8%/12,20*12,0,39394687)]

Is it possible to save this much on SIP for retirement Every Month??? Tiring isnt it??

I gave up calculating other Annuities as I understood well that those values are going to be even higher!

So, whats the solution for Retirement Fund? I will tell you our little own secret at the end!

Child Education Fund: http://healthywealthyhomemaker.blogspot.in/2012/12/how-to-fund-your-childs-education.html

Child Marriage Fund: 
http://healthywealthyhomemaker.blogspot.in/2013/01/childrens-marriage-fund-india.html