In insurance claims, a total loss or write-off is a situation where the lost value, repair cost or salvage cost of a damaged property exceeds its insured value, and simply replacing the old property with a new equivalent is more cost-effective.

Such a loss may be an "actual total loss" or a "constructive total loss". Constructive total loss considers further incidental expenses beyond repair, such as force majeure.

In a total loss, the insurer must indemnify the assured in full, and ownership of the insured item thereby passes to the insurer under the legal process of "subrogation". Although the policy determines the level at which the loss becomes total rather than partial, nevertheless the assured (and NOT the insurer) has the final say as to whether he wishes to make a partial or total claim.

If the insured item is, say, a car or a house, the policy will normally give it a "market value" which may be less than the assured had in mind; any disagreement would need to be challenged, perhaps using arbitration. In marine insurance, policies may be valued (where the value of the ship or cargo is agreed) or unvalued (where a market value at the time of the claim would need to be ascertained). In the absence of fraud, the Marine Insurance Act 1906 states the agreed value in a valued policy is conclusive, except in cases of constructive total loss, as in the cases of the cruise ship Costa Concordia and the ship The Bamburi.

Written off properties are usually demolished or torn down, scrapped, or recycled for parts after their policies are settled; so the insurer may be relieved not to have the insured item subrogated to him, as in Asfar v Blundell [1896].

Policies covering homes, vehicles, and other non-investment assets subject to depreciation may indemnify the insured to much less than the full replacement cost, so that the insured items may become "total losses" despite some residual value.

An actual total loss of a vessel occurs when repair is physically or legally impossible. A total loss may be presumed when a ship disappears and no news is received within a reasonable time. Some legal authorities do not consider it an actual total loss if repair costs are merely prohibitive, while others include cases where the cost of repair would exceed the cost of the vessel. In any case, the term "legally impossible" covers instances where reconstruction would be so extensive that the resulting craft would be legally considered a new vessel.

A constructive total loss is a situation where the cost of repairs plus the cost of salvage equal or exceed the value of the vessel. It also covers cases where the vessel has been abandoned in the reasonable belief that a total loss is inevitable. The calculation can be affected by environmental cleanup costs.