Agency invoicing software and a retainer invoice template that works
Short answer: Agency invoicing has to handle two things most generic invoicing tools weren't built around: a recurring retainer fee that repeats every month, and extras beyond scope that need adding on top without it getting lost. As of October 2026, QuickBooks Online's Simple Start plan is listed at $19 a month (a discounted rate for new customers, regular price $38) and Xero's Early plan runs $27 a month after an introductory discount period, both general accounting tools with solid invoicing. Harvest's Teams plan at $9 a seat a month generates invoices straight from logged time, which fits a retainer model more naturally. Productive bundles recurring budgets and invoicing into its Professional plan at $25 to $29 a user a month. The pricing promotions on QuickBooks and Xero specifically change often, so confirm the current rate before budgeting around either.
You want to invoice retainer clients correctly every month, including the extras, without errors creeping in or revenue quietly slipping through the cracks.
I'm Ranjit, and I run Blur Studio: 15+ years building software, 120 apps taken live, and clients who have gone on to raise $10M+. I build AI systems and processes that help businesses do a lot more with a lot less time. I also work differently from most of what else is out there, more on that further down this page. Say hello.
What makes agency invoicing different?
A freelancer or a shop usually invoices once per job. An agency on retainers invoices the same client every month for the same base fee, plus whatever extras came up that cycle, which is a genuinely different workflow than most generic invoicing tools are built around first.
- Recurring retainer invoices: The base fee needs to go out reliably every month without someone manually recreating it each time.
- Extras beyond scope: Work outside the retainer needs to be tracked and added to the next invoice, not forgotten because nobody wrote it down at the time.
- Multiple clients, consistent format: Clients compare notes sometimes. A consistent, professional invoice format across all of them matters more than it seems like it should.
- Payment terms and late follow-up: Automated reminders for anything that goes unpaid past the due date, so chasing payment isn't a manual task someone has to remember.
The best agency invoicing tools, compared
QuickBooks Online
QuickBooks Online, a widely used small business accounting platform, lists its Simple Start plan at $19 a month and Essentials at $42.50 a month, both shown as 50%-off introductory rates for new customers (regular prices $38 and $85) when I checked, so confirm the current non-promotional rate before assuming it'll hold past any introductory period. Simple Start supports unlimited invoices once QuickBooks Payments is enabled, and Essentials adds the ability to put employee time directly on invoices, useful for billing extras tracked by staff hours.
- Best for: Agencies that want invoicing bundled with full bookkeeping and tax-ready accounting in one widely supported tool. My QuickBooks alternatives guide covers Xero, FreshBooks and others if this doesn't fit.
Xero
Xero, an accounting platform similar in scope to QuickBooks, listed its Early plan at $27 a month and Growing at $59 a month at full price, though a steep introductory discount (90% off for 6 months, through a promotion expiring in early November 2026 when I checked) was active at the time, which will not reflect your ongoing cost. Growing supports unlimited invoices and quotes with automated bill entry, while Early caps at 20 invoices a month, tight for most multi-client agencies.
- Best for: Agencies that want unlimited invoicing without hitting Xero's Early-tier cap, and are comfortable budgeting for the standard rate rather than a time-limited promotion.
Harvest
Harvest, a time tracking and invoicing tool, generates invoices directly from logged time and expenses, which fits a retainer model more naturally than general accounting software built around manual line items. Its Teams plan at $9 a seat a month includes this, with integrations to QuickBooks Online, Xero and Stripe for payment processing, meaning many agencies run Harvest for time and invoice generation while keeping QuickBooks or Xero for the underlying bookkeeping.
- Best for: Agencies that invoice primarily off logged hours and want invoices to build themselves from that time rather than being typed up separately each month.
Productive
Productive, a work and profitability management platform built for agencies, bundles recurring budgets, meaning a retainer fee that regenerates automatically each billing cycle, into its Professional plan at $25 to $29 a user a month, alongside the broader project and profitability features covered in my agency profitability software guide. This is the most retainer-native option of the four, built specifically around the idea of a recurring fee plus extras rather than invoicing being bolted on as a generic accounting feature.
- Best for: Agencies that want recurring retainer invoicing built into the same platform as their budgeting and resourcing, rather than running a separate accounting tool.
How this differs from project-based invoicing
A lot of invoicing advice online is written for one-off project billing, deposits, milestones, a final payment on delivery, which is a different shape of problem than a recurring retainer. My invoicing app guide for contractors covers that project-based model in more depth if part of your agency's work is fixed-scope projects rather than ongoing retainers, since many agencies run both models side by side and need to invoice each one differently.
A retainer invoice template
Whichever tool you use, a clear retainer invoice usually needs these lines, kept consistent month to month so a client can actually compare one invoice to the last:
| Line item | Example |
|---|---|
| Retainer fee (Month, Year) | Monthly marketing retainer - November 2026 |
| Scope reference | Per agreement dated [date], covers [brief scope summary] |
| Extras beyond scope (itemized) | Additional landing page design - 4 hrs @ $150/hr |
| Subtotal | $4,600 |
| Payment terms | Due within 15 days |
The scope reference line is the one agencies skip most often, and it's the single easiest way to head off a dispute over why an extra was billed, since it points back to the original agreement rather than relying on everyone's memory of what was and wasn't included.
How to stop missed extras
The most common agency invoicing failure isn't a wrong number, it's a forgotten one: work genuinely done outside the retainer scope that nobody captured before the invoice went out, so it's written off for free by default. A simple fix that works without new software: whoever approves out-of-scope work logs it the moment it's agreed, in the same place time gets tracked, with a one-line note on what was asked and why it's outside the retainer. Reviewing that log before each invoice run, rather than relying on memory at billing time, catches most of what would otherwise get missed.
A worked example: 5 retainer clients
Say your agency runs 5 retainer clients, each paying $3,000 a month, with roughly 2 of them having a genuine out-of-scope extra most months. On QuickBooks or Xero alone, that's 5 invoices built manually each cycle, each needing the extras added by hand from whatever notes exist, which at this scale is manageable but relies entirely on someone remembering to check for extras before hitting send. On Harvest, if time is logged against each client with a clear "extra" tag, the invoice can pull both the retainer line and the extra line from the same time data automatically, reducing the manual step to a final review rather than building the invoice from scratch. At 5 clients the time saved is modest, maybe 20 to 30 minutes a month, but it compounds past 15 or 20 clients into a genuinely significant chunk of someone's week every billing cycle, which is usually the point agencies decide the switch to time-based invoicing is worth the setup effort.
How I'd approach this
For most agencies, QuickBooks or Xero plus Harvest for time-based invoicing is a solid combination, and Productive is worth a serious look if you want retainer billing built into the same platform as your budgeting from the start. Where a custom build becomes worth considering is when invoicing needs to pull from several systems at once, time tracked in one tool, scope agreements in another, and extras logged somewhere else, into one clean invoice automatically, rather than someone manually reconciling three sources every billing cycle.
Questions people ask
What's the best invoicing software for agency retainers?
Harvest or Productive fit a retainer model most naturally, since both can generate recurring invoices directly from logged time or a set recurring fee, rather than requiring a line-item invoice built from scratch each month.
Can agency invoicing be automated?
Yes, for the recurring base fee. Harvest can generate invoices from logged time automatically, and Productive supports recurring budgets that regenerate each billing cycle. Extras beyond scope still need a human to log and approve them before they're added.
Is QuickBooks or Xero better for an agency?
Both cover core invoicing and accounting well. Xero's Growing plan supports unlimited invoices from its entry tier more cleanly, while QuickBooks has broader third-party integration support. Check each one's current promotional pricing directly, since both had time-limited discounts active when I checked in October 2026.
How do I invoice for work outside the retainer scope?
Log it the moment it's agreed, with a short note referencing why it's outside scope, in the same place you track time. Add it as a clearly itemized separate line on the next invoice rather than folding it into the retainer fee, so the client can see exactly what the extra charge covers.
What payment terms should an agency retainer invoice use?
Net 15 is common for retainers, since the work is ongoing and cash flow matters more than it does for a one-off project. Whatever you choose, state it clearly on every invoice and follow up promptly once it's past due.
Roughly what does a custom invoicing workflow cost?
As a broad reference, fixes and finishes start at around $1,500, and new builds start higher, always a fixed price agreed in writing before I start, never an hourly rate. My AI app cost guide explains what actually drives a quote up or down.
Is my agency too small for this?
No. Most of the owners I work with have no tech team at all, that is the whole point. If the smarter move is a cheap software subscription instead of custom software, I will tell you that on the first call, even though it means I do not get paid.