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The life time of stored data depends on the storage density as well as the physical properties and microstructure of the media. Perpendicular media for ultra-high density recording needs to have high anisotropy to withstand thermal instabilities over long time. In this study, we used a micromagnetic model based on a scaling method to numerically calculate the percentage of magnetic decay caused by thermal fluctuations after ten years. Realistic grain configurations for 1 Tbit/in/sup 2/ and 125 Gbit/in/sup 2/ recording were used to seek the critical grain magnetization and anisotropy field of magnetic media that are thermally stable for ten years. For less than 10% decay, an H/sub K/ of 20 kOe and M/sub S//sup grain/ of 600 emu/cm/sup 3/ is required. Alternatively, H/sub K/ can be reduced to 16 kOe if M/sub S//sup grain/ is 800 emu/cm/sup 3/.