Q: I am thinking about starting a Roth IRA, in addition to my 401(k). At this point, I can afford about $100 a month. Or should I be all right for retirement with what I am doing now? -- J.C., Easton, Pa.

A: I think you'll agree that the Roth IRA is a good idea.

First, you will see the wisdom of starting early on retirement savings. If you continue at the current rate, including the company contributions, by the time you are 65 your rollover IRA and 401(k) collectively would amount to $900,385, presuming 10 percent average investment returns.

But the bad news is inflation. If it averages 3.5 percent, your balance would have the buying power of about $270,000 in today's money.

Your savings might be invested at retirement in a fixed-income portfolio earning 6.5 percent, which would bring you an income stream equivalent to about $17,500 a year in today's money. You might assume that when you combine that with Social Security, you would have enough. If I were you, I wouldn't be wildly excited about what Social Security may offer you in the year 2036.

Better to protect yourself now than to be anxiously watching the system.

However, if you add a Roth IRA with $100 monthly contributions, over the course of 35 years you would accumulate a further $340,116, following the same assumptions. That would give you a grand total of $1,240,531, about $372,000 in today's money.

From that, you might expect an income stream equivalent to about $24,180 a year in today's money, and more than 30 percent of it would be tax-free.

Finally, to further brighten the picture: If you add the Roth IRA, it would mean that almost 9.7 percent of your gross earnings would be going into your retirement savings. If you maintain your savings as a percentage of earnings, adjusting the dollars saved upwards each time you get a raise, your eventual accumulation would be far greater than the levels I have projected. That's good, because you have to measure a comfortable retirement in two ways: by how much money you will have on the first day of retirement, and by how well you are prepared to cope with inflation.