The primary difference between a regular and direct mutual fund is the expense ratio. Regular mutual funds have higher expense ratios due to additional fees, while direct mutual funds have lower expense ratios, leading to higher returns over the long term. For example, if Raj and Rahul both invest ₹5,000 monthly for 2 years in the same fund, Raj (who invested in a direct mutual fund) will make more money than Rahul (who invested in a regular mutual fund) because of the lower expense ratio in the direct fund.