Milestone Billing, Retainers, and WIP: What Project-Based Businesses Need to Watch Each Month

Your client pays a deposit before work starts. The team completes a phase before the next invoice goes out. A milestone payment arrives while substantial work remains.

These are normal situations for creative agencies, design studios, and architecture firms. They also explain why cash received, invoices issued, and revenue earned can tell different stories.

A monthly review keeps those stories connected.

1. Keep billing, earned revenue, and cash separate An invoice records a billing event. A payment records a cash event. Neither automatically establishes how much revenue has been earned under every accounting method.

Maintain a clear view of the amount billed, cash collected, work performed, and work remaining. For accrual reporting, revenue timing follows the applicable accounting method and contract terms. Cash-basis and tax reporting can differ.

Confirm the treatment with your accountant rather than assuming the invoice date or payment date always answers the revenue question.

2. Review work in progress and unbilled work Work in progress describes work underway. Unbilled work describes work or charges that have not yet been invoiced. An active project can have both billed and unbilled work, so do not treat the two labels as identical.

Keep an operational schedule showing each project's stage, completed billing triggers, approved additional work, and next invoice date. If a milestone is complete but the invoice is still pending, assign the next action to someone.

Not every WIP balance belongs on the balance sheet. The accounting treatment depends on the arrangement and reporting method. The operational schedule is still useful for spotting billing delays.

3. Reconcile retainer balances by client The word retainer can describe different arrangements. An advance for future services, a refundable deposit, and an earned fee for availability may require different treatment.

For advances tracked as liabilities in accrual books, review the opening balance, new receipts, amounts applied or earned, refunds, and ending balance. Match the ending balance to the supporting client records and contract terms.

Do not move an amount into revenue solely because cash arrived. Confirm the agreed treatment and document when amounts are applied. Keep a client-level record so the remaining balance can be explained clearly.

4. Compare milestones with actual project progress Review whether each contractual billing trigger has been reached, whether any approval is outstanding, and what work remains before the next invoice.

Billing schedules and delivery schedules do not always align perfectly. A project that has collected substantial cash may still face significant future labor and contractor costs. Another may have completed billable work but be waiting on administrative follow-through.

Looking at both schedules helps you plan the next phase and identify timing gaps.

5. Put costs and collections beside the billing schedule Review project costs to date, remaining delivery commitments, unpaid invoices, and expected receipts alongside milestone invoices and retainer balances.

For example, an agency may have collected a deposit but still need to pay a freelance team before the next milestone. An architecture firm may have completed a phase while a client approval delays the next invoice.

These timing gaps help explain cash flow pressure that a revenue total alone cannot show.

Make one monthly schedule do useful work For every active project, record its stage, amount billed, cash collected, remaining advance balance where applicable, unbilled items, next billing trigger, and next action. Reconcile the financial amounts to your books, while keeping operational estimates clearly identified.

That review gives you a clearer basis for billing follow-up and cash planning.

If you would like help organizing project billing and reporting in QuickBooks Online, email hello@smartvirtualsolutions.com.