This resource list from Propel Nonprofits includes considerations for reserve planning and some sample policies.
“Operating reserves may be a part of the organization’s unrestricted cash or working capital. Every nonprofit needs to have sufficient cash flow coming in from various income sources and going out to pay expenses and other obligations when they are due. Some organizations create reserves by setting aside cash in addition to the regular bank fund balances for use when regular cash flow is disrupted.
“Reserves are also different from restricted funds. Restricted funds are grants and contributions that have been received for specific programs or projects. These funds are “restricted” for use according to the grant agreement or donor’s instructions. Sometimes this means that restricted funds sit idle in the bank for a while and the nonprofit cannot use those funds for some other purpose.
“Reserves, on the other hand, are ‘unrestricted’ funds that can be used in any way that the nonprofit’s management and board chooses.