Imagine a dairy plant: you put milk into a process and out come cream, skim milk, and butter—all at the same time, from the same process. Nobody planned to make just one of them; they all emerged together. That's the core idea of joint products: two or more products of significant value that are simultaneously produced from a single common process, up to a specific point called the split-off point.
The split-off point is the moment in production where the joint products become separately identifiable. All costs incurred before this point are called joint costs (or common costs), and the central problem of joint product costing is: how do we fairly share these joint costs among the products? The ICAI curriculum recognises four main methods — (1) Physical/Output Method, where you apportion based on weight or units; (2) Sales Value at Split-off Method, where market price at split-off drives the split; (3) Net Realisable Value (NRV) Method (the most exam-heavy one), where you work backwards from final selling price after deducting further processing costs; and (4) Average Cost Method, used when units are identical in nature.
The NRV Method is the examiner's favourite. The logic: a product that fetches more value should absorb more of the common cost. NRV = Final Selling Price − Further Processing Costs (post split-off). You then apportion joint costs in the ratio of NRVs. A key distinction that trips students up: by-products are outputs with minor value compared to joint products. By-product income is typically credited to the joint process account (reducing joint cost), not treated as a separate product with its own cost allocation. This is tested frequently as a 5–8 mark numerical in Paper 4.