Current year's net income is a line that sometimes appears within the retained earnings section of a corporation's balance sheet, showing the amount of net income earned so far in the current accounting year, separately from the retained earnings balance carried over from all prior years. It exists because some accounting software does not automatically roll the current year's income statement results into the formal Retained Earnings account until the accounting year is actually closed out at year end.
Why the line exists at all
Many accounting systems keep revenue and expense accounts open and accumulating throughout the year, only transferring their combined net result into Retained Earnings through formal closing entries once the fiscal year ends. Until that happens, a company preparing an interim balance sheet partway through the year needs some way to show stockholders the cumulative profit earned so far, and "current year's net income" is the line used to display that running total without prematurely closing the books.
How it relates to total stockholders' equity
Current year's net income adds to total stockholders' equity in exactly the same way the prior years' accumulated retained earnings balance does, since both represent profit the corporation has earned and not yet distributed as dividends; the only difference is timing and presentation, separating this year's still-open results from the already-closed prior years' total. Once the fiscal year ends and closing entries are posted, the current year's net income balance is folded into retained earnings and the line disappears until the next interim period.