Q: I’d like to save $1 million in today’s dollars. But what will $1 million be worth in the future?

A: Investors worry about all sorts of flation.

Some fear government spending is going to force it to print dollars and flood the economy with money. That could cause inflation, or rising prices. Others fear the economy is stalling and consumers and businesses will save and not spend. If that happens, it could cause deflation, or falling prices.

So far, though, neither has happened. Prices have been pretty stable for many years. If you would like to see for yourself, you can poke around the Bureau of Labor Statistics website .

Yes, I understand there are some who question the government numbers. But that’s a topic for another time.

Instead, let’s see how inflation or deflation can affect your savings goals. Remember, when you say you want to save $1 million, you mean that you want the same purchasing power in the future as you’d get from $1 million today.

If there’s even mild inflation, $1 million of today’s dollars would be worth much less in the future. Assuming just 3% annual inflation over 30 years, if you had $1 million in the bank in 2040, that would only have the purchasing power of about $412,000 in today’s dollars. Inflation can severely erode the value of your assets over time.

But, let’s say we get deflation. If prices fall 3% a year the next 30 years very unlikely your $1 million in 2040 would have the purchasing power of $2.5 million in today’s dollars.

So, if you think we’ll get 3% annual inflation, to have the equivalent of $1 million in 30 years, you need to save $2.4 million in 2010 dollars. If you think we’ll get even more inflation than that, say 6%, you need to save $5.7 million in 2010 dollars. And if you expect 10% annual inflation, you’ll need $17.4 million to be a millionaire in 30 years.

On the other side, if you expect 3% annual deflation for 30 years, you’ll need to save just $401,000 to live like a millionaire in 2040.

Calculating these numbers isn’t the tricky part. The Bureau of Labor Statistics has a simple inflation calculator here. If you want to run sophisticated scenarios, you can try this calculator.

The hard part is predicting what’s going to happen in the future. You can read all sorts of economic forecasts that run the gamut from extreme deflation to hyperinflation. But even professional bond fund managers will tell you that predicting interest rates and inflation is difficult, if not impossible.

The safest bet would be to plan for 3.5% annual inflation, which is slightly higher than the historical average. In that case, today’s $1 million would only be equivalent to $356,000. Of course, your savings should be earnings something during the 30 years, so the gap won’t be as bad as it may appear at first glance.

If you earn an average of 3.5% a year on your $1 million, your buying power would stay even, with $2.8 million in 2040 dollars.

Matt Krantz is a financial markets reporter at USA TODAY and author of Investing Online for Dummies and Fundamental Analysis for Dummies. He answers a different reader question every weekday in his Ask Matt column at money.usatoday.com. To submit a question, e-mail Matt at mkrantz@usatoday.com. Click here to see previous Ask Matt columns. Follow Matt on Twitter at: twitter.com/mattkrantz