What invoicing software do agencies use to bill monthly retainers?

What invoicing software do agencies use to bill monthly retainers? It usually comes up on the first of the month, when the same twelve invoices have to go out again, one client has used more hours than the retainer covers, another has used fewer and wants to know where they went, and somebody has to remember which is which.

The short answer: agencies bill monthly retainers with invoicing software that raises the same invoice on a schedule, counts the hours against what the client paid for, and bills the overage without a fight. FreshBooks and Harvest have a dedicated retainer feature. Billbooks, Zoho Invoice, QuickBooks Online, Invoice Ninja, Wave and Bonsai use recurring invoices, and differ on hours, overage and payment.

Is this you?

• You copy last month's retainer invoice, change the date, and hope nothing else changed.
• A client asks how many of their hours were used this month, and the answer is in three places.
• The team worked past the retainer, and the extra hours were never billed because nobody wanted the conversation.
• One retainer invoice went out twice, or not at all, because two people both thought it was theirs.
• Your biggest retainer client pays when they get round to it, and that one invoice decides whether the month is comfortable.

Why retainer billing slips

A retainer looks like the easiest invoice an agency sends: same client, same amount, same day. That is exactly why it slips. Nobody owns it, because it is supposed to run itself, so it gets copied by hand, sent late, or sent without the overage that the account manager meant to add. The hours sit in a time tracker, the fee sits in the invoicing tool, and the only place they meet is somebody's memory at the end of the month.

The other half is habit. Agencies are good at scoping projects and bad at policing retainers, because raising an overage feels like nickel-and-diming a client you want to keep. So the overage is waived quietly, month after month, and the retainer turns into a discount nobody agreed to.

What it costs if nothing changes

Retainers concentrate an agency's income, which raises the stakes of every late or missed invoice. In our invoice data: For the typical small business, the single biggest client accounts for 43% of a year's billing (58 businesses with two or more clients). (Source: Billbooks invoice data.) If that client is a retainer, a retainer invoice that goes out on the tenth instead of the first is close to half your month waiting nine extra days.

Chasing is the part most teams skip. Only 3.3% of invoices carry an automatic reminder interval (2,026 of 61,185), set by 65 of the 271 businesses in the study. The most repeated piece of advice in invoicing is configured on one invoice in thirty. (Source: Billbooks payment-advice study.) A retainer is the easiest invoice there is to put a reminder on, because you set it up once.

Four tests for retainer billing software

Every invoicing tool says it handles retainers, because every one has recurring invoices. These four questions are what separate a tool that bills a retainer from one that only repeats an invoice.

1. Does the invoice raise itself, and can you check it first?

The basic job is an invoice that generates on the same day every month. The detail that matters for agencies is whether it can arrive as a draft rather than going straight to the client, so the account manager can add this month's overage or pass-through costs before it is sent.

2. Are hours counted against the retainer?

An hours-based retainer, say 20 hours a month for a fixed fee, needs the time tracked against it so you can see used and remaining hours mid-month, not at the end. Without that, the retainer is a fixed fee with a guess attached.

3. What happens to overage and unused hours?

Two questions your contract should answer and your software should follow: are hours over the retainer billed, and at what rate, and do unused hours roll over to next month or expire? Check what the tool does by default, because the default becomes your policy if nobody overrides it.

4. Can it take the payment automatically?

For a fixed monthly fee, a saved card or bank debit removes the chase altogether. Check whether automatic payment works on a recurring invoice, which payment methods it accepts, and what the client has to agree to first.

Which tools do what

From each company's own help and product pages, read in November 2026 and linked beside each entry. We list only what we checked, so a feature that is not mentioned here has not been checked, not ruled out.

• Billbooks bills retainers as recurring invoices, which are included on every paid plan. You set the cadence, from weekly to once every few years, run it open-ended or cap the number of invoices, and choose whether each one sends automatically or arrives as a draft for you to finish and send. Automatic reminders can follow at 7, 15, 30 or 45 days. Tracked time can be turned into invoice lines with your rate applied, or added to an invoice already in your drafts, which is how overage hours get onto this month's retainer invoice. What it does not do: there is no retainer balance, so prepaid hours are not drawn down and unused hours are not rolled over for you, and a saved card is not charged automatically when a recurring invoice goes out. Pricing is per business rather than per user, with users capped by plan: 2 on Basic at $7.95 a month, 5 on Standard at $14.95 and 10 on Professional at $29.95. See recurring invoices, time tracking and pricing.
• FreshBooks has the most complete hours-based retainer of the tools we checked. A retainer sets a fee per period, the hours per period and a rate for excess hours, then generates invoices on schedule, sent automatically or as drafts. Time tracked to the client is deducted from the retainer balance, and a retainer view shows hours logged against the budget. Two limits from its own help: unused time does not carry forward to the next period (FreshBooks suggests a prepayment credit if you want it to), and invoices for excess hours have to be generated by you. Each client can have one active retainer, and retainers are available only on the Plus, Premium and Select plans (FreshBooks: what are retainers). See Billbooks vs FreshBooks.
• Harvest treats a retainer as prepaid funds rather than a monthly fee. You raise a retainer invoice, its payment goes into the retainer's funds, and later invoices built from tracked time, expenses or fixed fees can draw from it. Its FAQ is specific about the edges: only Administrators can create and add funds to a retainer, an invoice saved without the retainer option cannot be edited to use it and has to be recreated, a new project cannot be added to an existing retainer, and retainer invoices are not copied to Xero or QuickBooks Online because the money is a liability until it is used (Harvest: retainer invoices FAQ). Harvest is priced per seat, from $11 a seat a month billed monthly before usage billing. See Billbooks vs Harvest.
• Zoho Invoice handles the hours side through recurring invoices: you can associate a project with a recurring invoice so its unbilled timesheet entries are invoiced to the client on schedule, every month (Zoho Invoice: projects on recurring invoices). Its current US help centre has no section on retainer invoices. Zoho documents those in Zoho Books instead, as a way to collect an advance payment recorded as a liability, with Unearned Revenue as the suggested account (Zoho Books: retainer invoices). See Billbooks vs Zoho Invoice.
• QuickBooks Online has recurring invoices, and a separate feature, recurring payments, that charges the client automatically on a daily, weekly, monthly or yearly schedule. Recurring payments need QuickBooks Payments turned on, and the client must consent within 30 days or the recurring payment expires. Intuit's help says that to start getting paid automatically you cancel the recurring transaction and send a recurring payment instead, and it still keeps recurring invoices available (QuickBooks: recurring payments overview). See Billbooks vs QuickBooks.
• Invoice Ninja runs retainers as recurring invoices, and its guide names the case directly: set remaining cycles to a fixed number for a fixed-term engagement, or Endless for open-ended retainers. Auto Bill can charge a saved payment method, with options to always charge, never charge, or let the client opt in or out at payment. Line items can carry date keywords such as :MONTH and :YEAR that fill in on each invoice, so a retainer line names the month it covers without anyone editing it (Invoice Ninja: recurring invoices). See Billbooks vs Invoice Ninja.
• Wave creates and sends recurring invoices on a schedule you set, and can bill the client automatically by card or bank payment on each one. Two conditions from its own help: automatic sending of recurring invoices is available to businesses that accept online payments through Wave or subscribe to the Pro Plan, and automatic recurring bank payments need the client to connect their bank through Plaid (Wave: set up a recurring invoice). We found no retainer balance or hours tracking in Wave's invoicing help. See Billbooks vs Wave.
• Bonsai has Retainer as one of four project billing types: you set a recurring fee and a cycle, weekly, monthly, quarterly, every six months or yearly, and project reports calculate revenue from the number of cycles and show costs and profitability per billing period (Bonsai: project billing types). That makes it a good view of whether a retainer is profitable. Bonsai is priced per user, with its invoicing tier at $25 a user a month. See Billbooks vs Bonsai.

What that adds up to

The choice comes down to what kind of retainer you sell. If it is a block of hours with a fixed fee and an overage rate, FreshBooks is the only one of the eight that models all three in one place, with the catch that unused hours do not roll over and overage invoices are raised by hand. If it is money paid in advance and drawn down as work is billed, Harvest's prepaid-funds model fits, and Zoho Books does the same in accounting terms.

If your retainers are a flat monthly fee, which is how most small agencies sell them, a dedicated retainer feature matters less than three ordinary things: the invoice raising itself on time, a draft step so the account manager can add this month's extras, and reminders or automatic payment so nobody chases. Billbooks, Zoho Invoice, QuickBooks Online, Invoice Ninja, Wave and Bonsai all do the first. They differ on the other two, and on whether you pay per business or per seat as the team grows.

What to do now, with what you already have

Write down, for each retainer client, three things your contract already says or should: what the fee covers, how hours over it are billed and at what rate, and whether unused hours expire. Then look at whatever tool you use today and set each retainer up once as a recurring invoice, as a draft if you add extras most months, with a reminder on it.

For the hours, pick one place where retainer time is logged and check it mid-month, not at the end. If you are over by the third week, tell the client then, while it is a scheduling conversation rather than an invoice dispute.

What to do if the overage has already gone unbilled

Do not back-bill months of waived hours in one invoice; that turns a good client into an argument. Bill the current month's overage at the agreed rate, with the hours listed so the client can see them. Then raise the pattern at the next account review: if the retainer is regularly exceeded, it is underpriced, and the fix is a new fee or a smaller scope, not quieter invoices.

How to stop it happening again

Give every retainer an owner whose name is on it, so no invoice is anyone's and everyone's. Put the overage rate and the rollover rule in the contract and in the invoice notes, so the client has read it before they see it charged. Set the recurring invoice and the reminder once, and review hours on a fixed day each month.

If you want the flat-fee version of that in one account, Billbooks recurring invoices raise each retainer on schedule, arrive as drafts if you want to add this month's hours from time tracking, and send the reminders for you, at one price for the business rather than per seat. It does not hold a prepaid balance, so if you sell drawn-down funds, the tools above that do are the better fit.

Two free tools for pricing and billing a retainer, no signup