Product
Overview
The commercial operating system for construction. Capture a commercial event once, every downstream workflow stays connected.
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Estimate & tender
Tendering
Documents & comms
DocumentsCorrespondence
Contract models
Fixed, cost plus & open book
Claim a fixed sum, reimburse at actual cost, or bill fully open book. ClaimStack handles each, the right way.
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Solutions
Overview
Built for every side of the contract. One commercial record the whole project team can trust, head contract to supplier.
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For subcontractors
Free to collaborate
Invited to a project? Submit claims and variations in a format that holds up, free forever.
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Resources
Overview
Practical guides on claims, variations and contracts, plus how ClaimStack connects, who's behind it, and how we keep your commercial data safe.
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See it on your project
A 30-minute walkthrough on your numbers, where the margin usually leaks.
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Pricing
Solutions/Contract models

Take on any contract. One system.

Fixed lump sum, cost plus, or open book, ClaimStack runs each with the same discipline. Bid the work, claim it the right way, and give clients the transparency they ask for, without a spreadsheet per job.

The business case for contract models

Your commercial model shouldn’t decide your software.

Most systems do one contract type well and force the rest into spreadsheets. So the cost-plus job runs on a side ledger, the open-book client waits on a manual reconciliation, and every model carries its own risk of error and dispute. ClaimStack supports fixed lump sum and cost plus natively, billed open book, so you can win and run any job on one disciplined process.

One contract type native, the rest bolted on the side.

01 Cost-plus jobs get tracked in a spreadsheet beside the system, then reconciled by hand.
02 Open-book clients wait on a pack of costs assembled from a year of receipts.
03 Each contract model carries its own workaround, so nothing is consistent across the portfolio.
04 What’s claimable under the contract is argued after the fact, not agreed up front.

Bid it, claim it, protect the margin

Claim against the agreed sum and cost breakdown, with variations captured and assessed as they arise. Because every change is on the record, the margin you priced is the margin you defend, cent-perfect from claim to certificate.

Cost breakdownVariations capturedCent-perfect
Progress claim 07 · Fixed lump sum
Main works · Building A
Cent-perfect
ItemContractTo dateThis claimPreliminaries$320,000$280,000$40,000Structure$1,150,000$1,050,000$150,000Facade$480,000$210,000$90,000Total$1,950,000$1,540,000$280,000
This claim$280,000
Less retention (5%)-$14,000
Due this claim$266,000

Reimbursables without the side ledger

Run a cost-plus job without a spreadsheet beside the system. ClaimStack aggregates the actual cost as it lands, adds your margin and monthly fee, and applies retention, so every dollar spent is billed and nothing is missed at the end of the month.

Actual cost capturedMargin billed in fullRetention
Cost-plus claim · June
Main works · open book
Cost + margin + fee
LabourFrom timesheets$84,200
MaterialsFrom receipts$46,750
SubcontractorsBy budget category$120,000
Cost this month$250,950
Builder margin (12%)+$30,114
Management fee (monthly)+$8,500
This claim$289,564

Transparency that wins the work

Open book is what many clients now ask for. Give it to them without the manual reconciliation: every claim carries a pack of the actual costs and their backing documents, so the reimbursement is transparent and straightforward to certify.

Full transparencyBacking docs attachedEasy to certify
Supporting documents · open book
Every cost, with its backing
Nothing gated
Timber supplyINV-4471$18,240✓ Attached
Crane hireINV-2210$9,600✓ Attached
Site labourTimesheet wk23$12,480✓ Attached
ConcreteREC-8890$6,300✓ Attached
4 documents attached$46,620
Two ways to run it

A workaround per model, or one that fits them all.

One model native, the rest in spreadsheets
—Cost-plus tracked on a side ledger.
—Open-book packs assembled by hand.
—A different workaround per job.
—Claimable scope argued after the fact.
Every model, one system
Lump sum and cost plus, both native.
Open-book packs built from the record.
One process across the portfolio.
Scope and variations agreed up front.

What one system for every model changes.

Bid any job with confidence
No side ledger for cost-plus
Open book that builds trust
Margin billed in full
One process, whole portfolio
Cent-perfect, either way

Frequently asked

Do you support cost-plus contracts?

Yes. Set the contract to cost plus and ClaimStack aggregates the actual cost as it lands, labour from timesheets, receipts and subcontractor costs by budget category, then adds your margin and monthly management fee, applies retention, and packages the monthly claim automatically.

What does open book mean here?

Cost-plus claims are billed open book. Each claim carries a supporting pack that shows the principal every actual cost with its backing document, receipts and invoices included, nothing gated, so the reimbursement is transparent and straightforward to certify.

Can one project use more than one model?

Yes. The delivery model is set per contract, so a single project can hold a mix, for example a cost-plus head contract alongside lump-sum subcontracts, all on the same connected record.

Is it Security of Payments compliant for both?

Yes. Whichever model the contract runs on, every claim is assessed and scheduled cent-perfect, with adjustments, reasons and a full audit trail, and statutory deadlines tracked.

Whatever the contract.
One system.