Mortgage rates are fundamentally unpredictable, you can't assume that they'll revert to a 30 year average. However what mortgage lenders do is "stress test" at

Mortgage rates are fundamentally unpredictable, you can't assume that they'll revert to a 30 year average. However what mortgage lenders do is "stress test" at 5%-6.5% that means they evaluate if you'd be able to afford to pay the mortgage + cover your essential costs (food, energy, etc.) if rates rose to those levels. It's essentially a worse-case assumption to ensure you wouldn't be bankrupt if that happened, not whether you'd be comfortably off at that level. If interest rates were to rise in 5-10 years time don't forget you could also remortgage to a longer time period to significantly reduce monthly payments if you needed to. Rates aren't going to jump overnight; if they rise it'll likely be a long slow-rise by which point you should have already paid down a meaningful percentage of your mortgage.