There is a consensus among the main political parties at Westminster that the UK should move to a fixed-term system.
Yet there is vigorous disagreement over the detail.
Why five-year terms?
Parliaments can already last for a maximum of five years, and Nick Clegg argues that there is a a "developing norm" that they last this long. To fix terms at five years balances the stability that governments need to "get on and do difficult things", says Mr Clegg, with the right level of accountability for voters.
Opponents point out that term length have been three years and 10 months on average since World War II, therefore the government's plans will result in fewer elections in the future. Governments become tired and aimless in the fifth year of a Parliament, argues historian Lord Hennessy. To fix at four-year terms would resonate better with the "natural bio-rhythm" of UK politics, he adds.
What if the government collapses?
The coalition wants there to be two ways to call an early election. First, if two-thirds of MPs vote for one. Second, if the government loses a vote of confidence by a simple majority in the Commons, MPs will have up to two weeks to form a new government from among their ranks. If they fail, an election ensues.
But Labour has complained that a vote of no-confidence will not automatically result in a general election in future, leading instead to the possibility of constitutional limbo. They also worry about the politicisation of the Speaker, who is meant to be impartial but will be required to certify whether a vote of no confidence has been passed or not. This is not always clear cut, they point out, noting that votes on key legislation in the past have sometimes been seen as confidence motions.
Does it matter if general elections clash with elections to the devolved institutions in Scotland, Wales and Northern Ireland?
With terms at the devolved institutions all fixed at four years, there will be a clash with the general election every 20 years under these plans, unless a parliamentary vote triggers an early election. Opposition MPs note that
a review into the May 2007 elections
in Scotland recommended that different elections should not be held on the same day again.
Initially, ministers dismissed this complaint - but have subsequently mooted solving the problem with an extension of the devolved terms to five years.