If you are an investor relying on stock dividends for income, you want to be sure that the company will be able to continue making the payments, and maybe even raise the dividend at some point.

Back in December, we published a list of dividend stocks for solid income while U.S. interest rates remain low. Since then, long-term interest rates have stayed low, with 10-year U.S. Treasury notes TMUBMUSD10Y, 0.701% yielding 2.14% on Tuesday, which was actually a pretty significant increase from 2.05% on Friday, as investors looked ahead to next week’s policy speech by Federal Reserve Chairwoman Janet Yellen.

The previous list included S&P 500 SPX, -1.11% companies with dividend yields of more than 3.5%, that had sufficient free cash flow over the previous 12 months to make it appear that the companies were well positioned to raise their dividends.

Free cash flow is a company’s remaining cash flow after capital expenditures. We can calculate a “cash flow yield” by dividing cash flow per share, for a particular 12-month period, by the share price. If the resulting figure is higher than the dividend, the company has “headroom” to increase the dividend.

This approach was suggested by Bill McMahon, the chief investment officer of Thomas Partners, back in May.

So what has changed since then we published our previous list in December? For one thing, 334 S&P 500 companies have had their 2015 earnings estimates cut since the beginning of the year. Two big reasons for this are the decline in oil prices and the rising value of the dollar EURUSD, -0.06% against the euro, which means higher prices for exports and declining sales for many companies.

So we thought it would be useful not only to consider the past 12 months’ free cash flow, but to look ahead using the consensus free-cash-flow estimates for 2015, among analysts polled by FactSet. This data isn’t available for every S&P 500 stock. But a list confined to companies for which the data is available indicates continued headroom to raise dividends is certainly a more conservative one.

Here are the highest-yielding S&P 500 stocks, with headroom to raise dividends based on the past 12 months and consensus 2015 free-cash-flow estimates:

Here’s the same list of companies, including industries and underlying data:

Do you hold shares of a company that is expected to see a significant decline in earnings or cash flow this year? If so, it doesn’t necessarily mean you should sell the shares, especially since the market is likely to have beaten you to the punch by pushing the share price lower. You need to do some extra research and consider not only the company’s prospects for growth of cash flow over the next few years, but also the health of its industry.

If you are looking to “buy more income” with a divided-stock investment, it’s very important to consider the likelihood of the company maintaining and even raising the dividend over time, and free cash flow needs to be a focus of your research.