A drop in donations over the past year has forced an animal rescue centre in Derby to launch an appeal to raise £100,000 in the next six months.
The Derby and District branch of the RSPCA faces increasing running costs but declining funding, managers said.
Trustee Sue Stevens said: "We are totally self-funded and if we cannot raise the money ourselves in the next six months we will not be bailed out."
The rescue centre cares for 60 cats and dogs, 17 rabbits and 35 other animals.
Ms Stevens said the centre depends on donations and legacies, but it is very difficult to predict how much income will arrive each month.
"We spend about £4,200 a week to keep the centre running, but sometimes it is literally hand-to-mouth.
"We could get a legacy for £50,000 next month and that would help us keep going - but we just don't know. It is a constant battle."
The centre has a long waiting list and is referring animals to other shelters in Nottingham and Staffordshire.