Richard Haldenby said he was "in shock" when he received an email detailing the price increase
Customers have shared their outrage after an app used by many businesses to track timesheets and produce invoices hiked bills by as much as 1500%, with one person calling it "daylight robbery".
Richard Haldenby, head of UK consultancy firm Salentis, told the BBC his monthly bill had risen from $130 (£95.50) to $2,110.
Others have reported similar price hikes online, with one person, external in the US saying their annual charge went from $2,800 to $23,000.
The BBC has approached Harvest for comment.
Harvest was acquired by the Italian tech company Bending Spoons in 2025, and changed its pricing structure the following year.
Many businesses who pay annually are only now finding out about the increase, as their payment is now coming up for renewal.
Haldenby, whose business consists of up to 15 staff in the UK at any one time, with sister companies also in the US and Australia, said he was "in shock" when he received an email detailing the price changes.
"We have used Harvest in our three companies for at least 15 years and have been loyal and enthusiastic advocates of it," he said.
"But if we were to accept this increase it would double our IT spend for the year, which is completely unaffordable."
Until the change, businesses paid a flat monthly fee for each user.
They could add or remove users as their staffing needs changed, meaning they only paid for the people who needed access.
Under the new usage-based pricing model, businesses can also be charged according to the number of active projects, clients and tasks they have – as well as the amount of revenue they invoice through the platform.
The email received by Richard Haldenby about the monthly price increase to use Harvest
Haldenby said he contacted the company to say his firm would not accept the change.