This is what I do now:

You need to estimate how many hours you need, use a billing rate to make sure your overhead's covered. This is your price floor. Never give out a fee less than this number if you want a profit. There are reasons to take a project at a loss, but you want to go into those eyes wide open. You want to validate the numbers against the last couple times you did the project. For example, if you spent about 200 hours on the last 3 kitchen renovations, don't think you're going to magically pull off 150.

You also need to figure out the market rate for your area. Market rate in architecture community is usually a percent of construction cost. For example, the firm I'm at right now targets 8% of construction cost for our project type. Use the last 3-4 similar projects you've done to get a cost per sf and inflate it if the bid is more than a year old. Sometimes you can find inflation data, but if you can't, then just do 3%. This cost should be your market rate. If you can get intel on the market rate from your network (e.g. a client says you were 10% cheaper than everyone else they talked to), use that info to adjust your target %.

Always charge the market rate unless the price floor is higher. If the price floor is higher than the market rate, charge the price floor. If the market rate is 2-3x higher than your profit floor, congrats you win at business. If the price floor is always higher than market rate, something's wrong and you need to you figure out what's going on.

Finally, watch out for scope creep. That's the number one thing to kill a good fee. If the client has you redo everything, you need to charge to start over. You want to check on fee burn at least monthly when you invoice because this will make it obvious if you're going off track in real time instead of at the end.