The bid form tells you how to submit a number. It also tells you, if you read it as a risk document rather than a template, who is going to pay when a quantity turns out to be wrong.
That second reading is the one that gets skipped. The pricing structure is treated as the owner's administrative preference, filled in as issued, and the risk it allocates is discovered on site.
What each form allocates
A lump sum transfers quantity risk to the contractor. You have priced the work as scoped, and if the excavation is deeper than the drawings implied, that is your problem to absorb or your change order to fight for.
A unit-price schedule leaves quantity risk with the owner. You have priced a rate, the owner has estimated a quantity, and the final payment follows what was actually measured. If the quantity doubles, you are paid for the quantity.
Neither is inherently better. They are different bets, and they call for different pricing.
1. A unit rate is not a lump sum divided by a quantity
The most common error in unit pricing is deriving the rate by taking a total price and dividing it by the estimated quantity. That arithmetic is correct only if the quantity is correct.
Fixed costs do not scale. Mobilization, setup, and the crew day you cannot subdivide are all recovered inside the rate, so a rate built on an estimated quantity of a thousand units is a losing rate at four hundred. Where the owner's estimate is soft, the rate has to carry that softness.
2. A lump sum is only as good as the scope boundary
Lump sum pricing depends entirely on the scope being closed. The risk is not that the work is difficult; it is that the boundary is ambiguous, and an ambiguous boundary under a lump sum resolves in the owner's favour by default.
This is where exclusions earn their place. A lump sum with a precise, written scope boundary is a defensible position. A lump sum with an implied one is an open account.
3. The hybrid is where it gets expensive
Most real tenders are neither. They are a lump sum base with a schedule of unit rates for specified items, and the interaction between the two is where money is lost.
The failure is double-counting or gapping at the seam. Work that sits inside the lump sum base is also listed as a unit-rate item, or work that belongs to neither is assumed to belong to the other. Both are invisible in the total, and both surface at measurement.
Walk the seam explicitly. For every unit-rate item, state whether the equivalent work is in or out of the base, and make the answer match what your exclusions say.
4. Provisional quantities and allowances
Provisional sums and allowances are the owner telling you the scope is not settled. They are useful information about the tender independent of their value.
The thing to check is whether the allowance carries your overhead and profit or is passed through at cost. That is stated in the front end and it is routinely different between two tenders from the same owner.
5. What to check on the bid form itself
Confirm the unit of measure against the specification, because they disagree more often than they should. Confirm the measurement method, since paid quantity is defined by how it will be measured, not by what is installed. Confirm whether rates are used to value change orders after award, which turns a rate you set casually into a rate that governs the whole job. And confirm how an arithmetic error between rate, quantity and extension is resolved, because the bid form usually says which one governs.
The decision is made before you price
By the time the estimate is being closed, the pricing structure is a given and the only remaining question is what number to write. The useful work happened earlier, when the bid form was first read and the firm decided what it was actually being asked to carry.
That is a bid/no-bid input as much as a pricing input. A unit-price tender with soft owner quantities and rates that govern change orders is a different proposition than the same job as a closed lump sum, and it may deserve a different answer.
Related reading: how to read instructions to bidders.
