Build a quote the right way round: start from your costs, add your markup and a buffer, and see the profit and margin before you send the number, not after the job is done.
A good quote starts with what the job costs you, then adds a markup for profit and a contingency for the unexpected. Add up labour, materials and other costs, pad it for the surprises, mark it up, and the price you land on is one you can actually make money at.
What the job actually costs you to do. Not the price yet.
The bit that turns a cost into a price worth doing.
A guide, not financial advice. Figures are estimates and ignore tax and VAT/GST. Always sense-check against your own accounts.
Here is the mistake that quietly costs trades a fortune. You add 20% to your costs, so you assume you are making a 20% margin. You are not. A 20% markup is only about a 17% margin, because the profit is a slice of the bigger, marked-up price, not of the smaller cost.
The calculator shows you both, so you always quote to the margin you actually want, not the one you think you are getting.
Almost no job goes exactly to plan. A wall opens up, a fitting is wrong, the old work is a mess. Contingency is a small buffer, often 5 to 15%, that stops those surprises eating your profit. If you do not use it, great, that is extra margin. If you do, you are covered instead of out of pocket.
Use this to work out your number behind the scenes, then give the customer a single, confident, fixed price for the job. You do not need to show them your labour rate or your markup. What they want is to know what it costs and that it will be done properly.