An unexpected overseas donation has helped Christchurch's Isaac Theatre Royal exceed its fundraising target.

It had to raise $150,000 through public funding in order to receive a matching grant from the Christchurch Earthquake Appeal Trust.

It ended up reaching about 122-percent of its target.

Chief executive Neil Cox says the funding will allow the theatre to pay its loan interest for the next 18 months

"We just don't want all of that to be eaten up with banks and insurance companies so it makes a lot more sense for us to have public donations to be able to put something aside and be able to actually help feed the arts and promote the arts in the city."