Since Donald Trump became the presumptive Republican nominee,several national polls have shown him narrowing the gap with his likely opponent, Hillary Clinton, or even leading.

But the election is more than five months away. When should you start to care about polls?

With some caveats, we believe the answer is: not quite yet.

The chart above shows how much the polling average at each point of the election cycle has differed from the final result. Each gray line represents a presidential election since 1980. The bright green line represents the average difference.

At this point – 167 days before the election – a simple polling average has differed from the final result by about nine percentage points. We expect this average to become more meaningful by the week, until the national party conventions temporarily make it less so, as shown in the bump about 100 days before the election. The average difference begins to flatten about two months before the election. The day before the voting, an unadjusted polling average has been about 3.5 points off the final result.

Of course, there are many ways to take an average. Our average, which has Mrs. Clinton leading by three points, looks at a somewhat longer time window at this stage in the race, making it a little slower to react to new polling information and less subject to sudden shifts in public sentiment. By comparison, the Huffington Post average has Mrs. Clinton up by 1.6 points. RealClearPolitics gives Mr. Trump the slimmest of leads. A more sophisticated method would probably include state-level polls, pollster house effects and adjustments for how states have voted in the past.

But this far out, a simple polling average is not particularly helpful at predicting the final result. (An analysis from the political scientists Robert Erikson and Christopher Wlezien concurs. That analysis focused on the correlation of polls with the final result, instead of the difference in percentage points.)

Of course, it’s better to be three points ahead in a polling average than three points behind. Mrs. Clinton will probably see her standing in the polls improve if, as expected, she wins the nomination, with some portion of Bernie Sanders’s supporters returning to the fold.

But there is still a long campaign season to go. Below, how the polling average changed in each election since 1980. We’ve highlighted party conventions and other meaningful dates in each cycle.

Mr. Trump’s recent bump probably reflects his emergence as the presumptive nominee; John Kasich and Ted Cruz dropped out of the race in early May. But there is almost always instability in the polling averages this far ahead of the election.

President Obama seemed to receive a bump in polls from the Democratic convention and the “47 percent” video of Mitt Romney released by Mother Jones. But polls tightened again in the month before the election. In 2012, Mr. Obama outperformed his polling averages on Election Day by about three percentage points.

In some ways, the 2008 election mirrors this race, with two Democratic candidates fighting over the party nomination after the emergence of a presumptive Republican nominee. At this point in that election, Mr. Obama and John McCain were nearly tied, but that was before Mr. Obama was the clear Democratic nominee. Once he was, he became the favorite. The most significant movement came in the closing months of the contest, amid the 2008 financial crisis.

John Kerry held a slight lead for a couple of months in 2004, but George W. Bush hung on to his five-point Republican convention bounce for a narrow victory.

With all of the controversy surrounding the 2000 election, and theFlorida recount in particular, it is easy to forget that the national polling average in November showed George W. Bush with a comfortable three-to-four-point lead over Al Gore.

But on Election Day, it was Mr. Gore who won the popular vote while losing the Electoral College.

Third-party candidates add an extra complication to presidential polling. Frequently, they perform well in polls early on, but their support tends to fall off.

In 1996, early polls showed the Reform Party candidate Ross Perot at 15 to 20 percent, a number that dwindled to 8 percent by Election Day.

You can see the well-defined convention bounces in 1996, as first the Republican and then the Democratic convention seemed to swing the polling average toward each party temporarily.

In terms of raw numbers, the 1996 election was the worst polling miss since 1980, with the Election Day average missing the final vote by over four points. But the ultimate result was never in doubt; Bill Clinton won by almost twice that margin.

The combination of the Democratic convention in July and Ross Perot’s abrupt departure from the race seemed to be responsible for a swing in polling average toward Mr. Clinton of over 20 points. Mr. Perot re-entered the race in October, but it did not substantially alter Mr. Clinton’s standing in the polls.

At this stage of the 1988 election, polls were very far from the final result, swinging a full 20 percentage points over the next five months, generally favoring George H.W. Bush after the Republican convention. Mr. Bush did win handily, as expected, though by a slightly smaller margin than polls predicted.

President Reagan led by double digits in most polls at every stage of his re-election campaign, but even these numbers swung wildly after Walter Mondale emerged as the Democratic nominee, and after both conventions.

he fluctuations in the polling average from the 1980 presidential election reflected uncertainty in both parties about the identity of their eventual nominees. Mr. Reagan did not clinch his party’s nomination until May 24. Poll averages did not stabilize until the last 40 days of the campaign, but they predicted a much narrower victory for Mr. Reagan than he ultimately received.

The 1980 contest is a good example of how a candidate’s standing in the polls can collapse.

Jimmy Carter led by around 10 points in early April.

A spate of polls in the week leading up to Election Day suggested that Mr. Carter might have narrowed Mr. Reagan’s lead – three of the nine polls released in the final 10 days of the campaign even showed Mr. Carter ahead – but ultimately, Mr. Reagan won handily.

When Should You Start Worrying About the Polls? Not Quite Yet