Marginal cost is the change in the total cost when the quantity produced is incremented by one. That is, it is the cost of producing one more unit of a good. For example, let us suppose:

Variable cost per unit     = Rs 25                  
Fixed cost                 = Rs 1,00,000
Cost of 10,000 units       = 25 × 10,000 = Rs 2,50,000
Total Cost of 10,000 units = Fixed Cost + Variable Cost
                           = 1,00,000 + 2,50,000
                           = Rs 3,50,000
Total cost of 10,001 units = 1,00,000 + 2,50,025
                           = Rs 3,50,025
Marginal Cost              = 3,50,025 – 3,50,000
                           = Rs 25