People aged 18 to 34 spent an average of $93 per person but believed others spent $112.
That was in sharp contrast to the over-65-year-olds who spent $59 on average and thought others spent $78.
Hartmann said young people often felt a lot more pressure and were inexperienced in Christmas spending and budgeting for it.
"I think there is a lot more pressure on consumerism at that age. The power of brands has a bigger impact."
Often younger people in their early working careers felt flush with cash in the short-term.
He said pressure and fear of not missing out was compiled by social media where people portrayed a highly edited version of their lives which did not reflect the highs and lows of reality.
The biggest gap between what was spent and what people believed others spent was found among Pacific Island people.
Those surveyed said they spent $97 on average but thought others spent $122 while the gap for Maori was $94 and $119.
Hartmann said he didn't know why those ethnicities felt others spent more but said Maori and Pacific people often said they felt pressure to spend more than they wanted to from family and their community.
"It's really hard for people to swim against the tide."
Hartmann also pointed to renters as being more likely to feel poorer when comparing their spending to others.
While the average spend for home-owners and renters was virtually the same at $82 and $81 there was a significant difference between what they believed others spent at $98 for home-owners and $108 for renters.
Hartmann said people needed to recognise that they were probably thinking a lot of people were doing more than they actually were.
He urges people to do their own thing when it came to present shopping.
"Make your own plans for your money and stick to them. Don't think so much about what others are doing."
He said people should consider making a list and setting a dollar amount and then comparison shopping online to get the best deal.
Secret Santas with a set dollar amount could be a good way to ensure a large group of people could join in the exchange of gifts without having it cost too much.
Hartmann said people could also save money by making presents themselves or buying secondhand.
There were no rules of thumb for how much people should spend on presents but Hartmann said people should base in on their own financial situation.
While it was easy to compare the monetary value of presents the value of a gift should not be equated to love.
"Just because more money was spent it doesn't mean more love."
TIPS TO KEEP CHRISTMAS AFFORDABLE
• Make a list (check it twice)
• Stick to a budget
• Compare prices online
• Try Secret Santa
• Don't worry about how much others are spending
• Consider making presents or buying second-hand