A third of people in the UK underestimate how many calories they are eating, according to an analysis of Office of National Statistics data.
It suggests British men eat more than 3,000 a day while claiming to eat 2,000. And women say they eat about 1,500 while consuming nearly 2,500.
The recommended daily calorie allowance is 2,500 for men and 2,000 for women.
The study of more than 4,000 people looked at energy expenditure and self-reporting information on food eaten.
Why the discrepancy?
Public Health England chief nutritionist Dr Alison Tedstone said under-reporting of calorie intakes "has always been a feature of all diet surveys".
"Some people forget what they've consumed and some change what they record knowing they are part of a survey.
"There's no way to get rid of under-reporting, but the steps we take to minimise it makes the National Diet and Nutrition Survey the most robust data on the population's diet."
As a rule of thumb, Public Health England recommends consuming about 400 calories for breakfast and 600 calories each for lunch and dinner to allow for extra drinks and snacks throughout the day.
But many cafes and restaurant do not have calorie information readily available and often include extra ingredients that add flavour but also calories.
Portion sizes vary
Some restaurant portions may also be bigger than ones eaten at home.
But portion size can also be an issue at home.
Many food labels state the number of calories in "one portion".
But the manufacturer's idea of "one portion" may not be the same as those dished up at the dinner table.
Snacks on the go
Many snacks also give calorie information, but this can be hard to understand and research suggests people spend just six seconds, on average, looking at food before buying it.
A large glass of wine can contain as many calories as a doughnut, and a pint of lager has about the same calorie count as a packet of crisps.
The average wine drinker in England takes in about 2,000 calories from alcohol every month.
Drinking five pints of lager a week adds up to 44,200 calories over a year, equivalent to eating 221 doughnuts.
Fizzy drinks and fruit juices contain sugars, and the amount of calories in a coffee bought at a shop with extras, such as syrup and whipped cream, can add up to the same as a desert.