Donors asking for a “good spending ratio” usually want assurance that money reaches the frontline. The filing metric to use is cause spend: charitable activities divided by total expenditure.
A common band for established UK charities is about 70–90%. Outside that range, ask whether the model explains it (grant-maker, shops, heavy public fundraising, volunteer-led) and whether the trustees’ report explains the year.
Chasing the lowest admin figure creates the starvation cycle. On CharityCompare, Financial Efficiency is capped at 20 of 100 Clarity Score points so ratios cannot dominate. See charity admin costs UK.