So many New Zealander's feel that they may never have enough lifetime wealth (see this article by Rob Stock at stuff.co.nz). To focus on the positive: at least they are thinking about a good question. How much money is required to life out the rest of one's days is the number that underpins most strategic financial planning. It's the node which links planning for life and disability insurance to planning for retirement.
Most people in the financial services industry have several ideas about this number: a kind of rough rule of thumb, some assumptions about what should or should not be included, and then a much more detailed number they have worked out in their own case - and therefore a clear idea on how to do so. Most other people, unless they are working with a good financial adviser, haven't got that far. Just trying to work out the number generates the right kind of context to work on all sorts of financial planning questions, which is one of the reasons this question is such a good one to address.
For those of us with a strong interest in life and health insurance, it is interesting because that figure for lifetime wealth is essentially the amount of money required in order to never need to earn an income again. That's a circumstance broadly equivalent to total and permanent disablement. It is also a guide to the level of wealth at which insurance may no longer be required - although it may still be desired, in order to protect that wealth.
Of course, it is slightly more complicated in many risk planning situations. Costs can be higher in the case of disablement compared to retirement, but the time horizon may be shorter - as those with chronic health conditions affecting their ability to work have lower life expectancy. In the case of the death of a family member future financial requirements are affected by both the loss of income and the loss of expenditure by the deceased. Variations abound. When financial planners talk about their approach to calculating this number I like to hear the details of how they calculate the amount, and intrigued to hear if they consider age-adjusted life expectancy in the process. If you are interested in further discussion on this do let me know, I have a number of resources available to share.