A clear signal that the general election will be over by this time next year was given by Prime Minister Lee Hsien Loong in his speech to 2,500 People's Action Party (PAP) activists on Sunday.

PM Lee, who is PAP secretary-general, told the PAP convention it could "well be the last time we meet, before the next general election". He said: "You have been working the ground for more than four years now, in some cases for more than half a century. Soon it will be time for battle again."

The next general election must be held by April 2021, at the latest. But PM Lee noted that it could be earlier.

Political observers who spoke to The Straits Times in recent months had said that December and the April to May periods were the most likely windows for a poll.

DECEMBER

But with the year drawing to a close and school holidays approaching, December is looking less and less likely.

The formation of the Electoral Boundaries Review Committee (EBRC) on Aug 1 was a clear indicator that the polls are near.

But there are several more steps before the election can be called, including the release of the electoral boundaries report.

In the past three general elections under PM Lee - in 2006, 2011 and 2015 - the time between the announcement of the EBRC's formation and Polling Day has ranged between two months and six months.

JANUARY

Given this precedent, the period before Chinese New Year festivities, which start on Jan 25 next year, is another potential window.

Factors observers cite in favour of this period: The opposition may be less prepared, and given the worsening economy, it may be wiser to call the election as early as possible to avoid the fallout from rising unemployment. But this ignores the elephant in the room: the Budget, which is usually delivered in mid-February. This year's Budget statement was on Feb 18.

LATE FEBRUARY TO MARCH

The Budget gives the Government a chance to announce measures to address worries on the ground and ameliorate cost-of-living issues.

Deputy Prime Minister and Finance Minister Heng Swee Keat said at the PAP convention that the Government will give details of its goods and services tax support package in Budget 2020, ahead of a tax hike some time after the general election.

Said Dr Felix Tan of SIM Global Education: "This reinforces in the minds of Singaporeans that they can expect something in the upcoming Budget."

Parliament has to wait a week from the Budget speech before its annual marathon sitting to debate the Budget over two weeks.

Time is then needed for presidential approval. This year, President Halimah Yacob gave her assent to the Supply Bill on March 13, days after it was passed in Parliament.

If that is the case next year, a general election could be called soon after that.

APRIL OR MAY

Considering the time needed for the measures from the Budget to sink in and benefit voters, April is a likely election window. Both the 2006 and 2011 elections were called soon after the Budget, in May.

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But one consideration could be avoiding major religious occasions.

The window for election in April is limited, as Good Friday falls on April 10 and polling is unlikely to take place that weekend.

But observers say it is also unlikely that the election will be called in May. The Muslim fasting month of Ramadan begins on April 24, with Hari Raya Puasa on May 24.

The Straits Times will be providing live coverage as Mr Heng announces the details in Parliament.

There will be livestreaming of his speech and a live blog on our website, as well as a Budget microsite and updates on our Facebook and Twitter accounts.

Readers can also sign up for e-mail updates of the proceedings.