Renovating in stages: commitments, payments and contingency without double counting

Splitting a renovation into stages can spread payments, but it does not automatically lower the cost. You need both a completion budget and a payment timetable. Work already paid, contracted work and optional work must remain distinct.

Give each cost a scope and a status

Record quantities, units, inclusions and prices. Label each item proposed, contracted, paid or removed. An advance payment belongs to its contract: adding both the full contract price and the advance counts the same work twice. The renovation contingency guide explains the basic components; this exercise adds stage-specific reserves and commitments.

Three fictional stages

These EUR amounts exclude tax and are examples, not quotes. Suppose preparation costs €2,000, installation €3,000 and optional finishes €1,000. Choose reserves of 10%, 20% and 10% purely to illustrate the calculation.

Stage	Base	Assumed reserve	Reserve amount
Preparation	€2,000	10%	€200
Installation	€3,000	20%	€600
Optional finishes	€1,000	10%	€100
Total	€6,000	15% equivalent	€900

Total contingency is the sum of each base multiplied by its rate. The total allowance is €6,900. The equivalent rate is €900 / €6,000 = 15%, not the unweighted average of the three percentages.

Reconcile what remains to be paid

You have paid €1,200 towards preparation. The installation contract is signed for €3,000 without a deposit, and finishes remain optional. Outstanding base costs are €800 + €3,000 + €1,000 = €4,800.

If you began with €7,000, cash after the advance is €5,800. Reserving €4,800 for remaining work and €900 for contingency leaves €100. Do not subtract the €1,200 twice or treat it as an additional cost above the €2,000 preparation budget.

Reproduce the total in Simuily

In the renovation calculator, use one item per stage, quantity one and the base amount in one cost component, leaving the others zero. Set other costs and tax to zero and the common contingency rate to 15%. The result should be €6,900.

This matches the total but does not store separate reserves. If you remove finishes, the remaining base is €5,000 and contingency €800: the equivalent rate becomes 16%, giving €5,800. Recalculate the weighting whenever scope changes. The calculator does not schedule deposits; keep due dates in a separate cash timetable.

Updating a stage without inflating the budget

If you approve a €300 extra and fund it from contingency, the base becomes €6,300 and unused reserve €600. The total stays €6,900. Keeping the full €900 reserve as well produces €7,200, which is appropriate only if you explicitly intend to replenish the reserve.

Check dependencies before postponing work. A delayed optional finish may be manageable, while delaying a prerequisite may change later quotes. Ask for updated scope, prices and payment dates rather than assuming the old offer remains valid.

Questions and limitations

Can I combine tax-inclusive and tax-exclusive quotes?

Not without normalising them. This calculator applies one tax rate at the end, including contingency. Different tax treatments require a separate item-by-item calculation; a common rate cannot reproduce all local arrangements.

Is unused contingency an actual expense?

It is an allowance, not a paid invoice. Report the authorised budget separately from final spending.

Before starting the next stage

Update outstanding base costs, unused reserve and due dates. Compare cash available before each deadline, not just the final total. The budget calculator helps assess periodic contributions. Commit to the stage you can fund with a clear margin and document what still needs a confirmed quote.