Fixed bid contracts are riskier than per hour contracts. There is the risk that you underestimate the project and have to work for free. There is also the rewar

Fixed bid contracts are riskier than per hour contracts. There is the risk that you underestimate the project and have to work for free. There is also the reward when you overestimate the effort, the client accepts the bid, and then you get paid for doing nothing. The key for being successful with fixed bid contracts is responsible estimation and communicating that to the client. For maintenance work it's almost always per hour unless you can negotiate a retainer policy. Back when I worked on contracts a not uncommon arrangement was a hybrid approach with the fixed bid deliverable and a pool of maintenance hours on the back end that were essentially options for the client.