There is no universally right answer. A fixed price suits a well-defined build, and it moves the risk of overrun onto your supplier. A day rate, sometimes called time and materials, suits work that is still taking shape, and it keeps you flexible while it does. The deciding factor is not which one sounds safer. It is how clearly you can describe what you want before the work starts.
Get the match right and either model works well. Get it wrong, and a fixed price becomes a fight over change requests, or a day rate becomes an open-ended bill. Most advice stops at picking the model. The part that actually protects you comes after that: knowing how each one quietly pulls on your supplier, and how to guard against it.
Key takeaways
- Fixed price and day rate are not good versus bad. Each suits a different situation, and how clearly you can describe the work up front decides which you can use.
- Fixed price suits a clear, agreed specification and moves the risk of overrun onto your supplier. Day rate suits work still taking shape and keeps you flexible while it does.
- If you cannot describe it clearly yet, do not pick a model. Start with a short paid scope that produces the specification, then price the build against it.
- Each model creates a pull on your supplier: a fixed price tempts padding and corner-cutting, a day rate tempts going slow. The day-rate pull is easily missed, because the invoice looks transparent.
- No contract removes those pulls. Trust is built by starting small and watching how a supplier behaves, and it protects you where the wording cannot.
What each model means, in short
Fixed price. You agree what will be built and what it will cost before the work starts. If it takes longer than expected, that is the supplier's problem, not your budget's. It only works when the scope is genuinely clear, because a fixed price is a promise against a specification. No real specification, no honest fixed price.
Day rate, or time and materials. You pay for the time the work takes, usually a daily rate for the people doing it. If the work grows or changes, the bill grows with it, and in exchange you can change direction as you learn without renegotiating a contract every time. The risk of the work running long sits with you, not the supplier.
This is the trade-off: fixed price buys certainty and hands the supplier the risk, whereas day rate buys flexibility and keeps the risk with you. Choose fixed price when you can describe the outcome precisely and want a number that does not move. Choose day rate when the idea is still forming and a fixed price would be a guess, which forces both sides to pretend they know things they do not.
We walk through both models with real examples, a fixed-price build and a day-rate one, in our guide to bespoke software costs. This post picks up where that leaves off: not which model to choose, but how each one can burn you once you have.
The pull each model puts on your supplier
The two models create different incentives for your supplier, and it is worth being clear-eyed about them so you know what to expect.
Under a fixed price the supplier carries the overrun risk, so the rational move is to protect against it. An honest supplier builds in sensible contingency. A more cautious one adds a larger buffer you quietly pay for, and under pressure to hold the margin, corners can get cut where you cannot see them.
Under a day rate the pull runs the other way. The longer it takes, the more the supplier earns, so some will work slowly or let the hours creep. This one is easily missed, because a day rate feels transparent. You can see the invoice, but not whether the work behind it took as long as it should have.
Neither pull makes a supplier dishonest. They are the incentives the models create, and no contract removes them completely. What does remove them is the thing a contract cannot buy, which is where this gets practical.
How to protect yourself
Simple conditions keep each model honest. For a fixed price, insist on a real written specification first, and read it; if a supplier will name a price without one, be more worried, not less. For a day rate, put a cap or checkpoints on it and agree what "done" means at each stage. Expect to see working software throughout, so you can always see where the money went and stop if the value is not there.
But safeguards only go so far, because the supplier still decides what to do with the incentive. The strongest protection is not clever wording. It is starting small, watching how a supplier behaves when the work is real, and building a relationship before you hand over anything that matters. A short paid scope or a small first phase tells you more about someone than any amount of due diligence on paper. Choose the model for the work, and the supplier for the relationship.
When neither is the right answer yet
Sometimes you genuinely cannot describe the build, and that is fine. The mistake is forcing a pricing model onto that uncertainty. The honest move is to start with a short, paid scoping phase whose only job is to produce the specification: what is in, what is out, and a firm price to build it. That is a small fixed-price step that turns a vague idea into something you can get a real quote for, from us or from anyone else. It is also where the wider question of what bespoke software costs stops being a scary range and becomes a number.
What to do next
Start with one honest question: can you describe what you want clearly enough to hold someone to it?
If you can, ask for a fixed price, insist on seeing the written specification behind it, and hold them to both. If you cannot, do not let anyone sell you certainty they cannot deliver. Get the specification first, and the price second.
If you are not sure which side of that line you sit on, that is the normal place to start, and it is exactly the thing we can help you work out. Tell us what you have in mind, and we will help you decide how it should be priced.