Wellington business consultant Tony Ryburn is making life easier for DIY share investors with a new online portfolio management tool designed to automatically calculate true returns and produce all data for taxation requirements.

Mr Ryburn said the system, Sharesight, was developed mainly for people who bought online and whose shares were not placed with traditional brokers.

"I had been messing around with shares and wanted to manage my own portfolio but found preparing for tax returns and the accounts of my family trust was a time-consuming nuisance," he said.

"Even worse, I did not know the true performance of my portfolio and did not have enough data to properly assess the performance of shares I might purchase in the future.

"So Sharesight came from personal frustration - a lot of people have only a limited idea of the true returns they get from shares they own."

Mr Ryburn said his system, built by software developers who also owned shares and backed by a database containing all New Zealand and Australian stocks, automatically provided earnings information including annualised gains and dividends.

"It also provides all the data needed to complete tax returns - it lists computation credits, dividends, withholding tax and separates Australian and New Zealand holdings.

"And amalgamations, splits, bonus issues and currency fluctuations are all taken into account. It is designed to be simple - enter the share, the number and date of purchase and all information is provided."

Mr Ryburn said Sharesight had been tested on a subscription-free basis since early this year - "and now we feel it's ready for the market," he said.