Justin Trudeau's honeymoon appears to be in full swing. After capturing just under 40 per cent of the vote in last month's general election, the most recent polls show that a majority of Canadians would now cast a ballot for the Liberal Party and consider Trudeau to be the best person to be prime minister.

But honeymoons come to an end. When will Trudeau's begin to wane?

According to a poll by Forum Research, the first to ask Canadians how they would vote in a new election, the Liberals have the support of 55 per cent, an increase of about 15 points from where the party stood on Oct. 19. Polling by Nanos Research shows that 51 per cent of Canadians name Trudeau as their preferred choice for prime minister, also up 15 points from Nanos's last pre-election poll of the campaign.

The scale of this immediate honeymoon is somewhat unusual, with the last time polling conducted after a federal campaign showing such a large increase for the winning party being in 1993, when the Liberals last returned to power after nine years on the opposition benches.

Subsequent polling may show more modest numbers as the initial enthusiasm surrounding the new Trudeau government subsides. International crises are already putting the new prime minister to the test. Past experience suggests, however, that Trudeau can still expect higher polling numbers for some time to come.

How other PMs fared in polls

If a honeymoon is defined as the period in which a party polls above its vote share in the election that brought it to power, it can vary in length dramatically. According to polling by Environics, Joe Clark's honeymoon in 1979 lasted a mere five months, while Stephen Harper's honeymoon in 2006 endured for seven. Brian Mulroney, however, saw his honeymoon last for about a year after his 1984 victory, while Jean Chrétien never scored under his 1993 electoral performance throughout his first term in office, which lasted just short of four years.

Honeymoons for re-elected governments tend to be shorter. With the exception of Chrétien (whose party always polled above its electoral performances), these honeymoons were as short as three months (Harper in 2008 and 2011) or as long as 10 to 12 months (Pierre Trudeau in 1980 and Paul Martin in 2004). Or, in the case of Mulroney in 1988, they can end as soon as they begin.

On average, however, these honeymoons have lasted an average of 16 months (or seven months, if we exclude Chrétien) since 1979.

But political honeymoons are not just about pleasing a few more Canadians than the number that voted for a party — they are primarily about a sustained increase in popularity. That has been harder to maintain.

Chrétien, for example, saw his party's popularity wane the closer he got to an election campaign, while many of the 'technical' honeymoons mentioned above were half as long in terms of when the polls started to turn sour: five months for Mulroney in 1984 and just three for Harper in 2006. By this measure, the average honeymoon lasted just 10 months — suggesting that Trudeau's numbers may begin to slip as soon as next summer.

Above average numbers for new PM

The Forum poll did not only have good numbers for the Liberal Party, but for Justin Trudeau as well. It pegged his approval rating at 60 per cent and his disapproval rating at just 20 per cent, the latter having been cut in half from where it was just before the election.

Those numbers are above average for a new prime minister. Early approval rating polling for new prime ministers since 1984 has averaged about 57 per cent, with disapproval averaging 27 per cent. Trudeau's score in the Forum poll puts him well ahead of Kim Campbell and Paul Martin, slightly ahead of Brian Mulroney and Stephen Harper, and behind Jean Chrétien.

Being a new prime minister is certainly better than being a re-elected one for popularity: re-elected prime ministers have averaged an approval rating of 48 per cent and a disapproval rating of 43 per cent after being returned to their jobs.

But based on past examples, Trudeau can reasonably expect to have a net positive approval rating for some time. Past prime ministers have seen their approval ratings remain positive for an average of 17 months after winning an election.

Approval and disapproval ratings of prime ministers from 1985 to 2015. Data from Environics pre-2009, quarterly averages of all polls post-2009. Click image for full size. The chart above, however, shows that approval ratings can swing wildly. Mulroney's approval ratings were very low between elections, but high when it came time to vote. Chrétien's were the opposite — soaring between campaigns but dropping as elections approached. Martin and Harper were unable to regain positive approval ratings after losing them.

History suggests that Trudeau will still have some time to enjoy his political honeymoon before the tide begins to turn against him. But which recent prime minister will be his model? Clark and Martin had short honeymoons and short tenures. Mulroney and Harper won multiple campaigns but were unpopular for much of their time in office. Chrétien dominated his rivals between campaigns and won three consecutive majority governments at the ballot box. It's clear which previous leader Trudeau would like to emulate, but the choice will not be up to him.

The poll by Forum Research was conducted for the Toronto Star, interviewing 1,256 Canadians via interactive voice response between Nov. 4 and 7. The survey carries a margin of error of +/- 3 per cent, 19 times out of 20.

The poll by Nanos Research was conducted for the Globe and Mail and CTV, interviewing 1,000 Canadians via telephone between Oct. 18 and Nov. 13. The survey carries a margin of error of +/- 3.1 per cent, 19 times out of 20.

This article reviews trends in public opinion surveys. Methodology, sample size and margin of error if one can be stated vary from survey to survey and have not been individually verified by the CBC.