After your first five years...

Beginning with the organization’s sixth year, the IRS will monitor your public charity status based on your public support as  reported on Schedule A, Public Charity Status and Public Support of your Form 990, Return of Organization Exempt From Tax.

You’ll have to show that you meet one of the public support tests over a five year computation period of the current year and the four preceding years.  If so, your organization will remain a public charity for that year and the next tax year.

More information on public charities and private foundations