A loan is borrowed money. Players can take out loans to pay for something that's not in the city budget. However, they'll be expected to pay it back with interest. It's a good idea only to take out a loan when absolutely necessary.
Loans became available in the SNES version of the original SimCity after the player earned the Bank reward. The player could take out a loan of $10,000. However, players had to pay back $500 each year, along with an extra $500 of interest.
SimCity 2000 has bonds instead of loans. Unlike loans in the other games, bonds are not paid back in installments. Instead, the city pays interest every year until the player pays back the original amount in full. Unlike other games in the series, the interest rate fluctuates based on the federal interest rate and the player's credit rating, and each bond has its own interest rate. The player can also choose to start a city with $10,000 bond with a 3% interest rate.
Loans in SimCity 3000 are handled differently. The player can take out up to ten loans at a time. They may also set the amount they take out in increments of §5,000, with a limit of §25,000 per loan. The player must pay back 150% of the total in regular payments over ten years.
SimCity 4 lets players take out ten-year bonds at an interest rate of 8.5%. Payments must be made each month. As the player successfully repays bonds, the amount they can borrow increases.
SimCity (2013) lets players take out loans at either §25,000, §50,000 with a town hall, and §100,000 with a department of economy. Unlike previous games, the player can only have a maximum of three bonds at the same time.