David Boyle, group manager investor education at the Commission for Financial Capability, said it was hard for people to picture what groceries were going to cost over such a long time frame.
"People know what they are buying on a day to day basis but to look at it over 30 years - it's just a lot harder to visualise."
But he said Kiwis were living longer and many could expect to spend 20 to 30 years in retirement.
A man who was 65 years old now could expect to live to an average age of 86 while for women it was 88 but average life expectancies were increasing at a rate of around one year for every five years a person had until age 65.
That could mean a 20 year old female today would live to an average age of 97 leaving them to pay for 32 years in retirement if they stopped working at 65.
Retirement spending - how much you'll need for:
Baked beans: $11,000
Toast: $10,000
Eggs: $4000
Toilet paper: $4000
Toothpaste: $3000
Chocolate: $17,000
Tea: $3000
Weetbix: $8000
Source: Commission for Financial Capability
But the good news was that people also underestimated how much they could have in KiwiSaver if they started saving at a young age.
An individual who joins KiwiSaver at the age of 18 and contributes 3 per cent from an average salary of $65,000 through their working lifetime could have between $300,000 to $400,000 by 65.
Of those surveyed 69 per cent believed they would have under $300,000 at retirement with 28 per cent estimating they would save under $100,000.
"KiwiSaver makes it easier for us to save for our futures, the trick is to work out what we need to do to make sure our income lasts as long as we do once we stop working," Boyle said.
The commission will also launch a new online tool on its money website www.sorted.org.nz to help people plan for their retirement this week.
More than 70 public events are planned around the country for Money Week which is now in its fifth year.
This year's theme is Show Me The Money and looks at how the costs of everyday items can add up over 30 years of retirement.
Check out www.moneyweek.org.nz for events in your area.
Coming up this week
• Tuesday: Biggest money mistakes made by millennials
• Wednesday: How lifestyle spending can ruin your money potential
• Thursday: Worst money mistakes to make in your 50s
• Friday noon online: Live chat with financial adviser Hannah McQueen from EnableMe. Send your questions to tamsyn.parker@nzherald.co.nz to have them answered by Hannah.