A financial commitment can help, but choose one you are actually willing to accept
Rewards pay after success; deposit schemes return your stake and add a reward. Among people willing to accept either, deposits raised success by about 13 percentage points. But only 13.7% accepted a deposit scheme versus 90% accepting rewards, so deposits help only people willing to use them.
What it takes
Deposit schemes put your own money at risk if you fail. The cited trial required US$150 upfront.
What you may gain
A US randomized trial of 2,538 employees and relatives or friends compared four incentives with usual care. Reward programs offering about US$800 had 90.0% acceptance; deposit programs requiring US$150 plus a possible US$650 reward had 13.7%. Six-month sustained abstinence ranged from 9.4% to 16.0% across incentive programs versus 6.0% with usual care. Overall rates were 15.7% for rewards and 10.2% for deposits. Among the estimated 13.7% willing to accept either type, deposit programs raised six-month cessation by 13.2 percentage points (95% CI 3.1–22.8) relative to rewards.
Context & considerations
The trial concerned smoking cessation; application to thesis writing or fitness is extrapolation, hence a medium benefit rating. A powerful scheme you will not accept is of no use to you. Choose an acceptable commitment; the author suggests starting with a small stake rather than none. For quitting itself, see cessation medicines.
Research & references
Halpern SD, French B, Small DS, et al. (2015). Randomized trial of four financial-incentive programs for smoking cessation. New England Journal of Medicine, 372(22), 2108–2117. https://doi.org/10.1056/NEJMoa1414293