When his regular supermarket ran out of the nappies his baby used, dad Blake Bennett rushed to a competitor, hoping to grab the essentials.
He realised then that several full-priced products at Woolworths were on special at Coles, and vice versa, and an idea was born.
Three years later, Mr Bennett has co-founded cost-saving website Grocerize.
"I realised I was saving $50 to $70 a week by splitting my shopping between Coles and Woolworths," Mr Bennett said.
He said his website could save shoppers 28 per cent on their weekly groceries.
The site was launched two weeks ago, and Newcastle's Mr Bennett said 20,000 users had visited so far.
"Grocerize continuously checks every item, instantly showing which store is cheaper for your shop," he said.
"You can dynamically split your cart between Coles and Woolworths, ensuring you pay the lowest price for each product."
Shoppers can use Grocerize to create a grocery list for in-store purchases or shop online directly through the supermarkets' websites.
The site compares live prices at both chains, incorporating any specials and discounts, and can send users sale alerts for their nominated products.
The start-up currently compares prices at the two major chains, but is considering expanding to include ALDI and IGA.
Retail expert Steve Kulmar said a grocery comparison website was a great idea to ease financial strain on consumers.
"We are living in an inflationary environment with tightening purse strings, mortgage rates going up, and people simply have less disposable, discretionary money to spend," Mr Kulmar said.
He said along with petrol, grocery shopping was one of the largest expenses for some households.
