If you do not pay a debt that you owe, you risk suffering not just financial penalties but damage to your credit rating. If a creditor reports the unpaid debt to a credit reporting agency, the agency may drop your score, making you look less creditworthy. This won't necessarily happen if you cancel your gym membership or end your contract early, however unpaid balances may go on your credit report.
Your credit report contains a record of all of your recent debts, both paid and unpaid. If you fail to pay back a loan on time or do not pay a bill, then this may end up on your credit report, causing your score to drop. For this to happen, however, the company to whom you owe the money has to report it to the credit reporting agency. This might happen in the case of a gym membership if you agreed to pay membership fees and then stopped paying them for no good reason.
The terms of gym memberships vary depending on the gym. Some gyms require that people take out memberships for a set period of time, but allow them to pay in a monthly installment plan. Others, however, allow people to pay month-to-month for membership or to pay for a long period of time in advance. If you sign up to pay a certain amount for membership and don't do this, the gym might take action to get its money and this may ultimately affect your credit score.
Gym membership contracts set out your cancellation options. If you stick to those, you shouldn't have any credit report problems. You may, however, have to serve out and pay a notice period, or you may have to carry on paying for membership until your contract is done. If you break the terms of your agreement, cancel your contract, and do not respond to requests for payment, then the gym may ultimately report you to a credit reporting agency or hand your debt over to a collections service to recover the unpaid balance. This might affect your credit score.
Even if you cancel a gym membership and leave a sum of money unpaid, you may not see any adverse effects on your credit report. An unpaid debt will only show up if the creditor or a collections agency reports it. If the bill for the gym is small enough, the gym may not consider it worth its time to chase payments and may instead just write it off.