The multimillionaire co-founders of Superdry have launched an innovative bonus scheme to share a fifth of their share price gains with the fashion brand’s 4,500 employees.

Julian Dunkerton and James Holder said they would share their share prices gains with all staff if and when the stock price hits a £18-per-share target. After that point they said they would transfer 20% of all gains to the new employee scheme.

If the shares rose by £5 above the £18 target the staff would share a £30m bonus. This would translate to a £2,000 bonus for the company’s 2,600 full-time shop staff and junior head office employees. Store managers would collect between £28,000 and £75,000, and executive team members would get at least £300,000. Part-time employees will also be included on a pro-rata basis. Board members are not participating in this scheme.

SuperGroup’s shares, which floated on the stock market at £5 in 2010, were changing hands at £15.70 on Tuesday. The scheme, which was launched at the company’s annual meeting in Cheltenham on Tuesday, will run until September 2020.

Dunkerton, who began his retailing career with a market stall funded by a £2,000 loan from his father in the 1980s, said it was important that all staff shared in the firm’s success.

“James and I passionately believe that the success of the Superdry brand is down to the combined work of all our people,” he said. “As the founders of the business we remain significant investors and it is important to us that we share our ongoing success with all colleagues.”

Dunkerton, 52, who is ranked by the Sunday Times as the UK’s 324th richest person with a £366m fortune, holds 26.7% of SuperGroup’s shares. He sold £53m worth of shares last year to pay for his divorce. Holder holds 10.6% of the shares.

Peter Bamford, SuperGroup’s chairman, said: “This plan is in keeping with the entrepreneurial spirit of SuperGroup, rewarding all our colleagues with a share of the value they help create.”

Dunkerton began his career selling clothes after his getting three Es at A-level put paid to his dream of being a doctor. He and Holder, who also started the Bench clothing brand, launched Superdry in 2003. The company now has 863 stores or concessions in 62 countries.

The brand got its big break when David Beckham wore one of its Osaka 6 T-shirts on the cover of his 2005 calendar. SuperGroup made a pre-tax profit of £84.8m in the year to 29 April – an increase of more than 53% on the prior year.

Dunkerton dismissed the suggestion that he was a “barrow boy made good”, and pointed out that his family, which owns the organic cider company Dunkertons, was middle class and he was educated at public school.

Superdry is known for smatterings of often-meaningless Japanese texts on its clothing. In 2011 the company told Japanese TV that it used a simple machine translation to generate Japanese text and it was aware that it often didn’tmake sense.

The SuperGroup employee share scheme comes soon after Sports Direct handed £43m in share bonuses to a group of nearly 2,000 permanent staff who took part in an incentive scheme launched in 2011.

However, the Sports Direct scheme provides rewards for only a small proportion of the 29,000 people who work for the firm who are eligible to participate.