Philip Hammond has been forced to defend the Office for Budget Responsibility (OBR) after pro-Brexit Conservative MPs attacked the independent organisation's economic forecasts.
The Chancellor's comment comes after the OBR estimated that the UK's GDP growth would slow to 1.4% in 2017, revised down from 2.2 after the UK voted to leave the EU.
Hammond, speaking a day after his Autumn Statement, told BBC Radio 4's Today programme that economic forecasting is "not a precise science".
"We should look at it as one of a range of possible outcomes we have to plan for," he said.
Hammond added: "We should have a plan which both invests in our economy and puts a little aside for the possibility of a slightly more rainy day next year or the year after."
The intervention came after Iain Duncan Smith, the former work and pensions secretary, accused the OBR of being an organisation that "simply hasn't got anything right" and described the forecast as "another utter doom and gloom scenario".
"We were told we would be in a recession. We are not. These predictions are worthless," he told The Telegraph.
Jacob Rees-Mogg, a member of the Commons Treasury committee, also said the OBR had been "particularly gloomy".
"One is that they assume that we will apply tariffs on the same basis inside the EU, which the Chancellor will know he will be able to remove. And secondly, they're particularly gloomy on the prospects for financial services," he told Sky News.