Tax season prep: get records in before the rush.

Good tax season prep starts months before the deadline. Most of the time a tax season costs goes on waiting for records, not on preparing returns. So the earlier the records arrive, the calmer the last weeks get.

This guide has two month-by-month plans:

• The US season, for 2026 returns: from October to the 15 April 2027 deadline.
• The UK Self Assessment season, for 2025–26: from September to the 31 January 2027 deadline.

Both cover who to ask first, when to send and what to do when a client is late anyway. The escalation steps, the weekly review and the late-client rules near the end work for either.

The US dates the plan works back from

Date	What's due
15 January 2027	The fourth estimated tax payment for 2026
1 February 2027	Employers and payers send W-2s and most 1099s (31 January is a Sunday)
16 February 2027	Brokers send 1099-B and consolidated statements (15 February is a federal holiday)
15 March 2027	Partnership and S corporation returns, and the Schedule K-1s their owners need
15 April 2027	Form 1040 and C corporation returns, any tax owed, and extension requests
15 October 2027	Individual returns filed on an extension

An extension gives more time to file, not to pay. State deadlines can differ. Checked on 24 October 2026 against When to file and Publication 509, Tax Calendars on IRS.gov.

Set your own deadline, well before the IRS's

Clients treat the date you give them as the real one. If you ask for documents "before 15 April", most will arrive in April. Give them your date instead.

• A records date for each batch. The end of January for business returns due on 15 March, and the end of February for individuals. This is the date clients see.
• Room for late forms. K-1s and corrected brokerage statements can arrive in March or later. Leave them open on the list, and don't hold up the rest of the request for them.
• An extension cut-off. For example, 31 March. Returns still missing documents then go on extension, under your late-client rules, below.

Say why the date is early. "We need March to prepare your return, ask you questions and get your approval before 15 April" is a reason a client can accept.

Sort your US clients into groups

Sending every request on the same day means every reply, question and upload lands in the same fortnight. Sort clients into groups first, then send one group at a time.

Group	Who's in it	When to send
Business	Partnerships and S corporations, due 15 March, and anyone whose payroll or 1099s you prepare	Early January
Main	W-2 employees with investments, homeowners, landlords, retirees and the self-employed	Early December
Waiting on K-1s	Owners of partnerships and S corporations, and clients with trusts or complex investments	Early December, with an extension in mind
Simple	Clients with a W-2 and little else, who reply quickly	Mid December
New	Clients who are new to you this season	As soon as they're on board

Stagger the records dates a few weeks apart. Documents then arrive in waves you can prepare as they come, not in one heap in March.

Month by month in the US, October to April

October and November: prepare

• Look back at last year. Who was late, who went on extension, whose K-1s arrived late, whose circumstances changed.
• Update your lists for 2026. Start from the Form 1040 document checklist and the small business tax return checklist, and keep a version per group.
• Fix your dates and rules. Records dates, extension cut-off, escalation, late-client terms.
• Prepare each batch. One request per client, with only the sections that apply and your records date.

December: send the organizers

• Send the main, K-1 and simple batches before the holidays. Clients then know what to keep when the forms arrive. The tax organizer email templates have wording for each.
• Remind clients who pay estimated tax that the fourth payment is due on 15 January.

January: business clients, and the first forms

• Send the business batch early in the month, with a records date at the end of January.
• Review uploads within a few days. W-2s and most 1099s arrive by 1 February. A wrong form caught now is a short email. Caught in April, it's a crisis.
• Start the weekly review (see below), even while numbers are small.

February: chase the individuals

• Chase by name once brokerage statements are out, after 16 February. Name the forms still missing.
• Prepare business returns as they complete. Don't wait for the whole batch to be in.
• Ask your questions now. Queries sent in February get answered before March gets busy.

March: the business deadline, K-1s and extensions

• File partnership and S corporation returns by 15 March, or extend them on Form 7004.
• Move owners' returns forward as their K-1s arrive.
• Apply your extension cut-off. Tell each client still missing documents that their return will go on extension, and that any tax owed is still due on 15 April.

April: file, or extend, by 15 April

• Get approvals and file. Most returns should be prepared by now and waiting for the client.
• File extensions on Form 4868 for clients still waiting on documents, with an estimate of what they owe.
• Note who was late. They go into next season's earliest batch.

The UK dates the plan works back from

Date	What's due
5 October 2026	Register for Self Assessment, if the client hasn't sent a return before or didn't need to for 2024–25
31 October 2026	Paper tax returns
30 December 2026	Online returns, if the client wants to pay their bill through their tax code
31 January 2027	Online returns, and the tax owed for 2025–26

A return filed late gets an initial £100 penalty, with more after 3 months. Paying late brings separate penalties and interest. Checked on 21 October 2026 against Self Assessment tax returns: deadlines and penalties on GOV.UK.

Set your own deadline, well before HMRC's

The same rule applies: clients treat your date as the real one. If you ask for records "before 31 January", most will arrive in January.

• A records date for each batch. Between the end of October and the end of November. This is the date clients see.
• An earlier date for tax-code clients. Their return has to be filed by 30 December, so ask for their records by the end of October.
• A cut-off for late records. For example, 31 December. Records that arrive after it are handled under your late-client rules, below.

Say why the date is early. "We need December to prepare your return, ask you questions and get your approval before 31 January" is a reason a client can accept.

Sort your UK clients into groups

The same idea, with the groups a Self Assessment season usually needs.

Group	Who's in it	When to send
Earliest	Tax-code clients, anyone with property sales, capital gains or foreign income, and last year's late clients	Early September
Main	Sole traders, partners and landlords	Late September
Simple	Employees and pensioners with a few statements, who reply quickly	Mid October
New	Clients who are new to you or to Self Assessment	As soon as they're on board

Stagger the records dates in the same order, a few weeks apart. Records then arrive in waves you can prepare as they come, not in one heap in December.

Keep each batch to a size your team can review within a week of it landing. New clients need their onboarding finished first; the client onboarding checklist covers it.

Month by month in the UK, September to January

September: prepare, then send the first batch

• Look back at last year. Who was late, who sent the wrong documents, whose circumstances changed.
• Update your lists for the new tax year. Start from the Self Assessment checklist and keep a version per group.
• Fix your dates and rules. Records dates, cut-off, escalation, late-client terms.
• Send the earliest batch. One request per client, with only the sections that apply and your records date.

October: send the rest and review as you go

• Send the main batch early in the month and the simple batch by the middle.
• Review uploads within a few days. A wrong document caught in October is a short email. Caught in January, it's a crisis.
• Start the weekly review (see below), even while numbers are small.
• Check for paper filers. Anyone still filing on paper has a 31 October deadline.

November: records dates land, so chase

• Follow your escalation steps as each batch's records date passes.
• Prepare returns as they complete. Don't wait for the whole batch to be in.
• Ask your questions now. Queries sent in November get answered before the holidays.

December: tax-code returns, and the cut-off

• File tax-code returns by 30 December. Their records should have been in since October.
• Call everyone still missing records before your office and theirs close for the holidays.
• Apply your cut-off. Anything still outstanding moves to your late-client rules.

January: file, and handle the late ones

• Get approvals and file. Most returns should be prepared by now and waiting for the client.
• Tell clients what to pay, and by when. The tax owed is due on 31 January, along with any first payment on account.
• Handle late clients one by one, using the rules you set in September.

Escalation: who does what, and when

Decide the steps once and let the dates trigger them. Then nobody has to judge when it's "time" to chase.

When	What happens	Who
3 and 7 days after sending	A reminder listing what's still missing	Automatic
3 days before the records date	A final reminder naming the missing items and the date	Automatic
2 weeks after sending with nothing uploaded	A phone call	The person who looks after the client
Records date passes	A call to agree what's missing and a new date	The person who looks after the client
2 weeks overdue	An email from a senior person, stating the cut-off and what happens after it	Partner or manager
Cut-off passes	Late-client rules apply	Partner or manager

A call is the right tool for silence. If two reminders get no reply at all, a third email won't find out why. The client reminder email templates have wording for each written step.

The weekly "who's stuck" review

Once a week, for 20 minutes, go through every open request with the people who look after the clients. Same day, same time, the same five questions.

1. Who hasn't started? Nothing uploaded a week or more after sending. Has the client even opened the request? Call them.
2. Who has stalled? Most things in, one or two items missing for over a week. Name the items, and offer another way to get them.
3. Who is overdue? Take each one to its next escalation step.
4. What's waiting for us? Uploads nobody has reviewed yet. The bottleneck isn't always the client.
5. What did we send back? Documents you asked to be replaced, and whether the client has seen the note.

Finish with a name and a date against each action. Keep a count of how many clients are complete, partly in and not started each week. The trend tells you early whether the deadline weeks will be busy or calm.

WEEKLY "WHO'S STUCK" REVIEW

1. Not started: nothing uploaded a week after sending.
   Opened the request? -> Call.
2. Stalled: one or two items missing for over a week.
   -> Name the items, offer another way to get them.
3. Overdue: past the records date.
   -> Next escalation step.
4. Waiting for us: uploads not yet reviewed.
   -> Review this week.
5. Sent back: replacements asked for.
   -> Check the client saw the note.

Each action gets a name and a date.
Count: complete / partly in / not started.

What to do with late clients

Some clients will be late whatever you do. What matters is that they knew the rule in advance and that you apply it the same way to everyone.

• Tell them early. Put your cut-off, and what happens after it, in the first request and the overdue email.
• Be clear about the risk. In the US, a return without its documents goes on extension, but the tax is still due on 15 April, and late payment can bring IRS penalties and interest. In the UK, if records arrive too late to file by 31 January, HMRC's penalties fall on the client. Say so plainly, and keep a copy of what you sent.
• Choose how you'll handle late work. For example, a late-work fee your terms allow for, or no promise of filing by the deadline once the cut-off has passed.
• Know when estimates may help. In the US, an extension needs an estimate of the tax owed so the client can pay on time. In the UK, GOV.UK explains when a return can include provisional figures, such as while waiting for a valuation, to be corrected later. Whether either fits a client is your professional call.
• Learn from it. Move this year's late clients into next year's earliest batch, or ask whether the engagement still works for you both.

How to do this in GarnerDocs

GarnerDocs handles the sending, chasing and weekly review in this plan, as the page on tax season for individual returns shows.

• A template for each group. Save a checklist for each kind of client, then start each request from the one that fits and remove what doesn't apply.
• A due date for each batch. Set the records date on each request. It shows how long is left, turns amber in the last 3 days and red once overdue, and the Requests page has Due soon and Overdue tabs.
• Batches as drafts. Prepare a batch's requests as drafts, then send them on the day the batch goes out. Drafts don't count towards your plan's active requests.
• The Needs your attention list. The Overview lists overdue requests, uploads waiting for review, clients with nothing uploaded a week after sending (and whether they opened the link), documents sent back and requests due within 3 days. Start your weekly review there.
• Reminders up to your date. By default, 3 and 7 days after sending and a final reminder 3 days before the due date, listing only what's missing. No automatic reminders go out after the due date, so that's where your call or Send reminder takes over. Custom schedules are on Growth and Pro.
• An owner for each client. Assign each request to the person who'll make the calls. They get its upload notifications and the client's replies.

See Due dates. Preparing a mix of US and UK returns? The tax preparers and advisors page covers both.

Sources

• When to file, IRS.gov. Checked on 24 October 2026.
• Publication 509 (2026), Tax Calendars, IRS.gov: due dates for Forms 1040, 1065, 1120-S and 1120, estimated tax, W-2s, K-1s and extensions. Checked on 24 October 2026.
• General Instructions for Certain Information Returns, IRS.gov: when 1099s and brokerage statements reach clients. Checked on 24 October 2026.
• Self Assessment tax returns: deadlines, GOV.UK (HMRC). Checked on 21 October 2026.
• Self Assessment tax returns: penalties, GOV.UK. Checked on 21 October 2026.
• Self Assessment tax returns: sending a return, GOV.UK. Checked on 21 October 2026.

This guide is general information, not legal or tax advice. Check the rules that apply to each client, including their state's.