Legal Invoice Calculator

An invoice that shows only a total invites a question the firm then has to answer twice. An invoice that shows time, flat fees, expenses, the discount applied and the retainer drawn down answers the question before it is asked.

This calculator assembles those components in the order they belong and reports both the invoice total and the amount actually due once client funds are applied.

Result

Invoice total

$6,861

Amount due

$2,861

Time fees: $6,290
Flat fee: $0
Discount applied: $629
Net fees: $5,661
Expenses: $1,200
Tax: $0
Retainer applied: $4,000
Retainer credit remaining: $0

This tool performs arithmetic on the values you enter. It does not provide legal advice and does not create an attorney-client relationship.

Showing the discount as a separate line makes the concession visible to the client rather than hiding it in a lower rate.

Tax treatment of legal fees and of disbursements differs by jurisdiction. Confirm which lines are taxable where you practise.

How to use the legal invoice calculator

Enter the billable hours and rate for the period, and any flat fee element.
Add expenses and disbursements.
Enter any discount percentage and the tax rate that applies.
Enter the retainer being applied, then read the amount due.

What people use this for

Building an invoice before entering it into a billing system.
Checking what a client will actually owe after a retainer draw-down.
Showing a discount explicitly rather than hiding it in a lower rate.
Reconciling a mixed flat-fee and hourly matter.

Worked examples

Every figure below is produced by running this calculator against the example inputs, so the numbers always match the tool.

A time-based invoice with a retainer applied

18.5 hours at $340, $1,200 of expenses, a 10% discount, no tax, with $4,000 of retainer applied.

Invoice total: $6,861
Amount due: $2,861
Discount applied: $629

A mixed invoice

A $3,500 flat fee plus 6 hours of out-of-scope time at $340, with a $2,500 retainer applied.

Invoice total: $5,990
Amount due: $3,490
Time fees: $2,040

Show the discount as a line

A concession delivered by quietly reducing the hours recorded is invisible, and an invisible concession earns no goodwill. The same reduction shown as a discount line is a visible act of judgement that the client can see and value.

It also protects the rate. A discount is a one-off decision about one invoice; a quietly reduced rate becomes the expected rate on every invoice that follows.

Retainer draw-down is not a discount

Applying a retainer reduces the amount due, not the amount billed. Conflating the two on an invoice makes both numbers harder to follow and makes trust accounting reconciliation harder than it needs to be.

Showing the invoice total, then the retainer applied, then the balance due keeps the client fund position clear - which matters, because how those funds are held is a regulated question in most jurisdictions.

Methodology and assumptions

What this calculator does, and what it deliberately does not do.

Time fees are hours × rate. The discount applies to fees only, not to expenses.
Tax applies to net fees plus expenses combined. Which components are taxable differs by jurisdiction.
The retainer is applied last, against the invoice total, and any excess is reported as remaining credit.
The tool performs arithmetic or date counting on the values you enter. It does not interpret a rule, a statute or a contract.
Nothing you type is transmitted or stored - the calculation runs entirely inside your browser.

This website provides general informational and productivity tools and does not provide legal advice or create an attorney-client relationship.

The date and deadline tools count days exactly as you instruct them. They do not interpret court rules, statutes of limitation, filing requirements or any other legal authority, and they do not know the rules of your jurisdiction.

Always verify any date, fee, or calculation against the governing rule, the court calendar and your own professional judgement. If you need legal advice, consult a lawyer licensed in your jurisdiction.

Frequently asked questions

Should tax apply to disbursements?

It depends on the jurisdiction and on whether the disbursement was incurred as agent or as principal. Confirm the treatment where you practise.

Can I apply more retainer than the invoice total?

The calculator caps the applied amount at the invoice total and reports the remainder as remaining credit, which is how a trust ledger would treat it.

Should I discount or write down?

A write-down happens before the invoice and is invisible to the client. A discount is shown. Which is appropriate depends on whether the reduction is a concession or a correction.

Is this a compliant invoice?

No. Invoice content requirements differ by jurisdiction and frequently include specific narrative, tax and regulatory details. This calculates amounts only.

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