Invoice Flow app icon Invoice Flow management Get the app
EN

How I Stopped Selling My Time and Started Selling Outcomes

By Thomas Gray, Management Consultant — Chicago, IL

I left a Big Four consulting firm in 2018 with fifteen years of management consulting experience, a strong professional network, and a billing model that I assumed would transfer directly to independent practice. The Big Four model is simple: bill by the hour, staff by the project, charge what the market will bear.

What I discovered is that the hourly model works well for a firm with 40 consultants. For an independent consultant, it has two structural problems.

The first problem: hourly billing creates a ceiling. You have a fixed number of hours. When you’re fully booked, the only way to earn more is to raise your rate. You’re always selling time, and time is finite.

The second problem: hourly billing misaligns incentives. Clients notice, consciously or not, that every question they ask costs them money. They ration their access to you. The relationship becomes transactional rather than advisory.

My first four independent projects were hourly-billed. They were professionally successful. The clients got what they needed. I got paid, sometimes after a longer wait than I’d have liked. But the income was lumpy — feast and famine — and I had no visibility into the next month.

I rebuilt the practice around outcomes. It took about two years.

The Shift to Project-Based and Retainer Billing

After the fourth hourly project, I made a deliberate decision: I would quote projects at a fixed project fee tied to outcomes, not hours. And I would convert clients who had ongoing needs into retained advisory relationships.

The project fee structure:

Project Engagement Rates:

The advisory retainer structure:

The Project Engagement Invoice

Invoice Flow app invoice editor of a management consultant — an implementation-support phase as a fixed fee plus reimbursable travel with project, phase and PO number in custom fields
The implementation phase as a fixed fee, travel reimbursed — with the PO their PMO expects.

For project engagements, I use three-phase milestone billing:

Strategy Consulting — [Company Name] — Project Initiation:

Each phase invoice references the SOW and shows the full structure. Clients see that they’re progressing through a defined engagement, not buying unlimited time.

For large enterprise clients:

Management Consulting Services — [Enterprise Name] — [Date]:

The Advisory Retainer Invoice

Monthly advisory retainers auto-invoiced:

Strategic Advisory Retainer — [Company Name] — [Month Year]:

The engagement highlights line is not a timesheet — it’s a reminder of the value delivered that month. Clients who see brief descriptions of what advisory time produced are more likely to renew than clients who see a fee with no context.

Scope Change Invoices

Invoice Flow app documents of a consultant — paid discovery and strategy phases, the implementation phase sent, a due-diligence project and a board-advisory draft
Discovery paid, strategy paid, implementation billed — the whole engagement, phase by phase.

Projects expand. When they do, I document scope changes before doing the work:

Scope Change Authorization — [Company Name] — [Date]:

The authorization signature on the scope change invoice prevents retrospective disputes about whether the additional work was approved. I’ve had one scope dispute in four years. The invoice documentation resolved it in twenty minutes.

Due Diligence and Transaction Support

Invoice Flow app expense tracker of a management consultant with billable flights, hotel, an industry report and an expert-network call tagged to clients
Flights, hotel, a research report, an expert call — each tagged to its engagement for passthrough.

M&A and transaction advisory work is priced on complexity:

Due Diligence Consulting — [Company Name] — [Date]:

The NDA reference on the invoice creates a documentation chain. If there are later questions about information handling, the invoice itself shows that the engagement was covered under the NDA.

Six Years Independent

Current practice metrics:

Year one of independent practice: approximately $180,000 annual revenue on hourly billing. Current year: on pace for approximately $600,000. The work is largely the same in quality. The billing model is fundamentally different.

The independent consulting career that looked uncertain in year one is now the practice I intended to build.

What InvoiceFlow Does for Management Consultants

Management consulting billing complexity — project milestone invoicing with SOW references, advisory retainers auto-generated monthly, scope change authorizations before work begins, enterprise PO fields, and transaction advisory with confidentiality documentation — is handled from one InvoiceFlow Android app.

Download InvoiceFlow. Build the three-phase project invoice template. Set up retainer billing for advisory clients. Issue scope change invoices before doing the work. The billing infrastructure supports the practice you want to build.

Thomas Gray is a management consultant in Chicago, Illinois, providing strategy development, operational improvement, M&A due diligence support, and strategic advisory services to mid-market and enterprise clients.