U.S. investors are bullish on the stock market, but they’re not showing it by increasing their 401k savings.

That lack of follow-through is a shame, as even a 1% hike in your monthly 401(k) savings plan can add up to $330 per month in your retiree “paycheck” down the road.

This figure comes from Fidelity Investments, which is chiding Americans these days about not saving enough for retirement, even though eight out of 10 investors believe the Standard & Poor’s 500 Index will rise by the end of the year.

However, there is some progress for Americans with their retirement accounts. According to Fidelity, 401(k) plan balances rose 11% recently to a nationwide average of $80,600. And if you have been working for a company that offered 401(k) plans for the past 10 years, the average balance number leaps to $211,800—up 19% from a year ago.

But in a recent report from Fidelity on U.S. workers and their 401(k) plans, company analysts say Americans are costing themselves income in retirement by being stingy on their retirement plan contributions now.

Says James MacDonald, president of workplace investing at Fidelity: “While it’s a good sign that some workers are increasing their savings for retirement, many younger workers—especially  Millennials—aren’t saving at the recommended 10% to 15% of their income. It is critical young workers realize that even the smallest increase to their monthly savings today or just 1%, whether in a 401(k) or an IRA, could have a meaningful impact on their retirement paycheck down the road.”

Here is how that translates into real dollars:

Say you’re 25 and have a salary of $40,000, and you added just $33 per month to your 401(k), with an assumed average annual rate of return of 7%. Fidelity says you could add $330 (in pretax income) to your monthly “retirement paycheck” by doing so. Even if you scaled back to an average annual rate of return of 5.5%, a 1% uptick in savings translates into an extra $200 every month in retirement.

If you’re 35 and make $60,000 annually, and you add $50 to your monthly 401(k) contribution, an average 7% annual rate of return will yield an additional $270 every month after you turn 65, or an extra $180 at a 5.5% annual rate of return.

Those are real dollars, and they really add up during your golden years. But that only holds true if you play the game right and start contributing that extra 1% every month, Fidelity says.

Do that and you’ll gain some much-needed momentum on your way to becoming a 401k Millionaire – on your terms, and no matter what your employer does.

As always, good luck, and good 401k savings – and I’ll see you next week.

Brian O’Connell is an investment analyst at Investing Daily, and the editor of the 401K Millionaire. An ex-Wall Street bond trader, he has appeared as an expert financial commentator on CNN, NPR, Fox News, Bloomberg, CNBC, C-Span, CBS Radio, and many other media broadcast outlets, and is the author of two best-selling books on retirement investing.