Why did my project cost more than the contract price?

Variations are the biggest cause. Each one may be small, but dozens add up. Without a register, the total shows only at the final account.

Delay adds time related costs for the contractor. If the delay is yours, you pay. If it is theirs, they pay.

Provisional sums and allowances can also run over. They are estimates, not fixed prices.

To find the cause, list every change with its date, source and cost. Then compare the total with the final account.