That's fraught will all sorts of biases. What if your shopping habits changed? eg. you started becoming more health-conscious and started buying healthier (and more expensive) foods. The BLS accounts for all of that by measuring the price of a fixed basket of goods, which mitigates those effects. The same can't be said of your budgeting spreadsheet. Or maybe your area is undergoing gentrification and the discount supermarket got replaced with a whole foods. Your grocery spending might have went up 50%, but that doesn't mean it's a meaningful representation of what's happening across the country.