Things that go "Boom!" get our attention. Sparklers are pretty, but firecrackers make our hearts race. Literally or metaphorically (explosive anger, a stock market crash), it's the four-alarm fires that make us jump. And big monsters like Godzilla or King Kong make a big impression.

In investing, though, it's the subtle changes that are most devastating. A ho-hum event like gradual inflation becomes a retirement snatcher, stealing away your ability to provide for yourself.

Inflation doesn't lead the nightly news or make for an arresting photo montage -- it's an abstract, pointy-headed economics term that's about as exciting as drying paint. It's the air slowly leaking from your tires. But inflation's effect on your future is as devastating as a blowout on a busy highway.

So, is inflation running your portfolio to the shoulder of the road?

Decaf dollars
Do you remember what a tank of gas, a loaf of bread, and a movie cost 10 or 20 years ago? Those were the days, right? The effect of inflation (the gradual tendency of prices to increase over time) makes for interesting cocktail party chatter.

Today it might seem criminal to charge $4 for a latte, but we can afford it, so we pay. At even half that price, our grandparents would have gone bankrupt buying a cup of joe each morning.

If Gram and Gramps were still in the workforce today, they probably wouldn't wince when the barista rang up their order. Because their salaries would have kept up with the cost of living.

But their investments would have withered. Years of diligent savings -- $100 a month for 20 years earning 8% -- would come to $60,000. That's a lot of lattes, but don't order a double shot just yet.

Put yourself in their shoes (that same investment scenario -- $100 a month for 20 years earning 8%). Sixty grand in 2027 dollars ain't gonna buy you what it can now. Nope, the spending power of your hard-earned money two decades from now will be cut in half. That's inflation's way of saying, "Thanks for your patience all these years. Here's a check for $30,000."

That decaf soy latte can quickly become a financial burden for those living on a fixed income.

When $1 million isn't worth $1 million
Historically, inflation has run between 3% and 4%. Using the Rule of 72 (sorry, another pointy-headed concept), that means the purchasing power of a dollar is cut in half every 18 to 24 years.

It's a slow burn -- one that's easy to overlook when you're focused on the snap, crackle, and pop of your investment returns.

Case in point: Say you start now with $2,000 in an S&P 500 index tracker such as the SPDR Trust (AMEX:SPY) and add $250 each month to your investment in giants such as Johnson & Johnson (NYSE:JNJ) and Intel (NASDAQ:INTC). If the market keeps up with its historical annual average of approximately 10%, you could have $1 million in about 35 years. But in 2042, if inflation were to keep up at a 3% pace, $1 million would only buy you $355,000 worth of stuff in today's money.

What does that mean in real-life terms? A while back, our Rule Your Retirement (click here for a free peek) newsletter illustrated the life cycle of a couple from age 22 to death (age 95). It showed that even with lower expenses in retirement (lower or no mortgage, no more child-rearing costs), the household needs more money for a 30-year retirement than it did during the couple's 43 working years.

So going back to our original example, in order to end up with $1 million in inflation-adjusted dollars, you'd have to up their initial investment to $10,000 and add about $700 per month. After 35 years, you'll have about $2.8 million, or about $1 million in inflation-adjusted dollars in the year 2042.

Defy the effects of gravity
OK, so you don't have tens of thousands of extra dollars to deploy. On to Plan B.

Supersizing your savings isn't the only way to keep the ravages of inflation at bay. How you deploy your investment dollars over the years (the asset-allocation part -- again, not the sexiest of financial topics) is just as critical to making sure your finances don't need emergency resuscitation when you're already retired.

Specifically, research shows that the conventional wisdom of moving the majority of your money into "safe" fixed-income investments such as bonds or Treasuries as you get older can be dangerous for your long-term spending power. The key is to balance volatility and risk, and not overweigh the latter. (The Rule Your Retirement column that discussed this offers a "sanity-check" formula to help perfect your portfolio's mix of equities and fixed instruments.)

Savers scared that their money won't be able to cover the occasional latte have two additional strategies at their disposal:

  1. Continue saving: Retirement doesn't automatically mean the end to saving and growing your wealth. Again, tweaking that mix of stocks and fixed-income investments will help you keep up with those whippersnapper investors. Keeping the income stream open is also a way to boost savings. Increasingly, more retirees are going back to work because they want to.
  2. Live on less. Scaling back seems like an obvious piece of advice. But being flexible with the all-important retirement withdrawal rate may be your ticket to keeping up your standard of living.

Stop inflation in its tracks
Inflation. Asset allocation. Withdrawal rates. (Is that paint I hear drying?)

Granted, these aren't the head-turners of the money world. But when ignored, they can silently kill your long-term dreams.

For Rule Your Retirement subscribers, accounting for the retirement snatchers is easy. The DirectAdvice online Financial Planning Tool is a comprehensive planning guide that will show if you're on track to meet your financial goals, covering everything from retirement savings to funding your kid's education to having enough insurance. The tool saves your information, offers advice (which you can then bandy about with us and other subscribers on our dedicated discussion boards), and helps you track your progress.

If you're not already a subscriber, grab a free copy of the newsletter. While you're at it, test-drive the DirectAdvice tool. If you find a leak in your retirement plan, we'll help you change the tire.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.