덧셈 is a tax refund service for business owners, employees, and part-time workers. It helps users easily find hidden refund amounts by utilizing competition among tax accountants. The service considers various tax deduction items and application methods, tailoring the refund amount based on individual circumstances. Additionally, users can opt for post-payment processing if immediate payment is burdensome.

One of the key features of 덧셈 includes a comprehensive 5-year income tax inquiry, automatic submission of user income data to participating tax accountants, automated refund amount calculation, review and input of refund amounts by participating tax accountants, auction-style selection of tax accountants, and tracking of refund progress and final details.