Elections to the devolved legislatures could be separated from general elections by up to six months, ministers have said.
The concession comes after Plaid Cymru and the Scottish National party attempted to change the length of the fixed-term parliaments currently being considered from five to four years.
Under present plans elections to Holyrood, Cardiff and Stormont will fall on the same day as general elections to the Westminster parliament every 20 years - starting in 2015.
Plaid's Jonathan Edwards proposed shortening the term to four years and won Labour support for his proposals, but his amendment was defeated in the Commons by 315 votes to 242.
The fixed term parliaments bill currently contains plans for a one-month separation between elections. The government has now agreed to consult on extending the separation period to six months.
"I am very pleased that the UK government has finally accepted our sensible argument that elections to the National Assembly for Wales should not be held on the same day as the UK election," Mr Edwards said afterwards.
"They told me that they would begin tomorrow with consultation with the Welsh government to ensure a compromise which would allow the Assembly to vary the date of the next Welsh Assembly election so that it does not clash.
"This is an excellent victory for Plaid Cymru and the SNP who have been campaigning hard for fair democracy for Wales and Scotland."
Mr Edwards' arguments about switching from a five-year to a four-year fixed term did not meet with a positive response from ministers, however.
He accused the coalition of choosing five years for political means, pointing out that three years and eight months is the average length of parliaments over the last 200 years.
"It appears to be a decision made from political expediency, and that is not in the best interests of the electorate or democracy," Mr Edwards told MPs.
Labour shadow justice minister Chris Bryant agreed with the four-year term.
"The government would have at least three good sessions in which they could advance their legislative cause, and if they wanted to do difficult things in the first and second years but retain their ability to recover their position in time for an election after four years, they would be able to do so," he said.
But constitutional affairs minister Mark Harper rejected the proposal outright.
He told the Commons: "The government strongly believe that a five-year fixed term is right, not only for this parliament but for subsequent parliaments, as it will provide the country with the strong and stable government that it needs."