How much you need is subjective question. The two truest answers are:
- You need more than you think.
- You need much less than you think
For some people it’s all about the minimum that you need to get by – hence needing less than you think. That’s the ultimate truth. We really don’t need all the things that we think we need. However, most people end up “needing” more than they think. As much as many of us try to be frugal, for most people there is inevitable lifestyle creep. Sometimes, it’s unavoidable like children (while children themselves may be avoidable, the additional cost of providing for them isn’t). For others, it’s just the inevitable spending increases that go along with income increases.
Nobody knows what’s going to happen in the future, but we should know where we are now. I think it’s always good to have a simple estimate of what one would actually need to retire tomorrow if you had to. I use the most basic of models - a present value estimate assuming a life expectancy, estimated annual expenditure, expected inflation, and expected investment growth rate. My number: 1.823 million and some change
How do I come up with this number? For those who aren’t familiar with present value, present value is simply the dollars needed now to have X dollars in Y years. For example let’s say I needed 20,000 in 3 years for down payment, I wouldn’t actually need 20,000 today. I would only need $17,276 right now assuming I could get a return of 5% annually (and not have to pay taxes on the interest). As of today, I shouldn’t have much of a problem getting a 3 year CD that pays around 5%. I would m$17,276 into a CD, and have the $20,000 in three years as needed.
Present value calculations reflect the fact that a dollar today is inherently worth more than a dollar tomorrow. Calculating what I need for retirement is not much different from calculating what I would need for a down payment. Instead of a single payment that I would need in three years, in retirement I would effectively need a payment every year to match what my expected expenses should be.

The one thing to note in the calculation above is what I actually use for the “rate”. Typically the rate is the discount rate or interest rate. If I weren’t making an adjustment for inflation I would’ve used 9%, the expected investments growth rate. However since I’m trying to take inflation into account, I need to adjust it.
i = inflation, r = growth rate
That adjusted rate = (1 + r)/(1 + i) - 1 = 5.83%
At first thought which was my first thought, the adjusted rate might be just be r - i. It’s not however for the same reason something that’s marked up 50% and then discounted 50% doesn’t return to the original price. If something that costs a dollar is marked up by 50%, it’s $1.50 and then subsequently discounted 50% it become .75 cents. Like discounts and markups, the effects of inflation and growth are multiplicative, not additive.
So back to my 1.8 million number. For myself I’ve assumed life expectancy of another 70 years, inflation of 3%, investment growth of 8.5%, and expenses of $100,000. The adjusted rate = (1+8.5%)/(1+3%) - 1= 5.34%. In Excel the formula is simply PV(5.34%, 70, 100000). Voila, 1.823 Million (actually negative 1.823 Million since the convention is to express the value as how much you would need put into (-) an investment)
If planning for retirement were truly this simple, everyone would know exactly how much to save. The biggest problem with using any simple model like this is the absolute certainty that is built into the model. Do I really know what inflation will be? Or how my investments will grow? For example if the first year my investment only grows 3%, but I spend the full 100,000, my whole plan would be derailed even if everything else continued as planned. I would’ve spent money that would never get a chance to grow. All the caveats aside, a simple model such this still does serve as good basic benchmark, and everyone needs a basic benchmark.