The tax for that year can be audited -- and assessed -- at any time. Most records, however, must be kept by the taxpayer for only three years after the tax return is filed. That is the general law on record keeping. There are documents, especially involving real estate, which you should keep forever. Special Rules For Real Estate. When you buy real estate, whether your principal residence or an investment property, clearly you have to keep your records for at least four years from the date you sell that property.