Sunk cost effect
Having already put money, and less reliably time or effort, into something, people are more likely to carry on with it.
Four of the eight page areas.
Four ways to use it, and one to avoid.
- Offer paid memberships, delivery passes, deposits and prepaid credit, which encourage repeat use.
- Remind customers what they have already paid for.
- Save progress in multi-step flows.
- Put easy steps first in multi-step flows, but expect less from effort than from money.
- Avoid: adding unavoidable fees late in checkout, as drip pricing has been banned under the DMCC Act 2024 since 6 April 2025.
A moderate effect for money already spent, with weaker evidence for time.
The meta-analysis of money already spent excluded time and effort investments.
A meta-analysis of 98 effect sizes found a moderate effect for money already spent (d = 0.50), and Many Labs replicated a sunk cost scenario across 36 samples (d = 0.31). Soman argued time is not treated like money, but a replication by Petrov and colleagues found sunk time costs had an effect too. Arkes and Blumer's full-price theatre subscribers attended more, but only for six months.
Six sources, each checked.
Last reviewed
Use to help people finish, not to trap them in flows that are hard to exit. Adding unavoidable fees late in checkout (drip pricing) has been banned under the DMCC Act 2024 since 6 April 2025: the first price shown must include all mandatory charges.
This is simply a pointer to check, not legal advice. Seek legal advice before you put this principle into action.