Pay per gym visit or for short periods until you have a year of consistent attendance
In three years of US data, members choosing contracts over US$70 monthly attended only 4.3 times monthly, paying over US$17 per visit when a ten-visit pass cost US$10 per visit. They overpaid about US$600 during membership. Unless you already have at least a year of steady attendance behind you, the source recommends paying per visit or making a short commitment.
What it takes
A single visit may cost more than an annual membership's advertised per-visit price. Estimate your real monthly attendance honestly.
What you may gain
A study followed 7,752 members at 3 US clubs for 3 years. Contracts above US$70/month averaged 4.3 visits, costing over US$17 each versus US$10 with ten-visit passes. Average excess spending was US$600 over membership. Monthly-contract members were also 17% more likely than annual-contract members to remain enrolled beyond a year.
Context & considerations
One US study, but the tendency to overestimate future self-control is broadly relevant. With at least a year of reliably attending twice weekly or more, an annual membership may indeed cost less.
Research & references
DellaVigna S, Malmendier U (2006). Paying Not to Go to the Gym. American Economic Review 96(3):694-719. https://doi.org/10.1257/aer.96.3.694