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Estimate your Self Assessment tax bill

Test site This is a test site with dummy HMRC services. Do not enter real personal information. How it works.

Try it yourself

Warning This is a test site. Use only the test customers. Do not enter real personal or financial information.

Dummy services on this site

Dummy services and whether this site uses them
Service Stands in for Used by this site
Dummy GOV.UK One Login Signing in to customer accounts Yes
Dummy HMRC APIs HMRC records and the Self Assessment account Yes
Dummy GOV.UK Notify inbox Emails to customers Yes
Dummy DVLA Company car details Yes
Dummy Budget Payment Plan service HMRC's Budget Payment Plan service No
On this test site the HMRC data feeds start switched on, so the calculator offers to fill in answers from HMRC records. An administrator can change that.

Example organisations

Each uses the calculator a different way. See how each one is set up.

Test customers

Choose one of these at the dummy GOV.UK One Login or the dummy HMRC sign-in. Each is based on a persona whose figures were worked out by hand.

Test customers and what to try
Customer Situation What to try
Sam OkaforSK 12 34 56 A
sam.okafor@example.com		 Employee with a buy-to-let flat. His pay and tax come from HMRC; he adds his rent and costs. (based on P26) Estimate his bill. Say yes to HMRC records and choose Sam at HMRC.
Grace WilliamsGW 23 45 67 B
grace.williams@example.com		 Pensioner. Her State Pension and bank interest come from HMRC; she adds her workplace pension. (based on P07) Estimate her bill for 2026 to 2027 with HMRC records.
Maya KowalskiMK 34 56 78 C
maya.kowalski@example.com		 Construction subcontractor. The CIS deductions her contractors reported come from HMRC. (based on P17) Estimate her bill with HMRC records. She is due a refund.
Nina ShahNS 45 67 89 D
nina.shah@example.com		 Parent earning £65,000. Her pay, Child Benefit and student loan plans come from HMRC. (based on P51) Estimate her bill with HMRC records: pay, Child Benefit and student loans are filled in.
Yara HughesYH 56 78 90 A
yara.hughes@example.com		 Employee with an electric company car. DVLA gives the car's fuel type and CO2 emissions. (based on P13) Try the company car API with registration YH25 EVC.
Jack MorganJC 22 33 44 C
jack.morgan@example.com		 Low earner who gives part of his Personal Allowance to his wife. HMRC records show the Marriage Allowance. (based on P10) Estimate his bill with HMRC records: Marriage Allowance is filled in.
Asha PatelAP 67 89 01 B
asha.patel@example.com		 Sole trader who has sent her tax return. Her bills and payments are on her HMRC account. (based on B01 and P15) Set up a plan in the dummy Budget Payment Plan service and answer the questions.
Kai BrownKB 78 90 12 C
kai.brown@example.com		 Sole trader with the same bills as Asha and £500 of credit on his account. (based on B12) Set up a plan in the dummy Budget Payment Plan service straight away.
Cara JonesCJ 89 01 23 D
cara.jones@example.com		 Still owes £250 from her July payment on account, so she cannot set up a Budget Payment Plan yet. (based on B04) Try to set up a plan. She owes overdue tax, so she cannot.
Ben CarterBC 90 12 34 A
ben.carter@example.com		 Sole trader who has not sent his tax return yet, so his bill is worked out from his answers. (based on B03) Set up a plan. He has not sent his return, so he is asked about his income.
Gita RaoRG 11 22 33 B
gita.rao@example.com		 Employee who keeps an account. Her pay so far, her bills and £200 of credit come from HMRC. (based on B01 bills) Sign in to an account with GOV.UK One Login and get her figures from HMRC.
Una NovakHR 33 44 55 D
una.novak@example.com		 Freelancer who signs in with GOV.UK One Login and uploads her bank transactions. (based on B21) Sign in to an account with GOV.UK One Login and upload bank transactions.
Olu AdeyemiOA 44 55 66 A
olu.adeyemi@example.com		 Uses an email address and password, so his emails (confirmation, password reset) go through Notify. (based on accounts) Create an account with a password. Find the emails in the dummy Notify inbox.
Leah ParkLP 66 77 88 A
leah.park@example.com		 Picture framer who also lets a flat. She has used Making Tax Digital for Income Tax since April 2026. Her bookkeeping app sends her quarterly updates, and HMRC holds an in-year calculation. (based on MTD personas)
Rita MensahRM 55 66 77 C
rita.mensah@example.com		 Administrator of the example organisations. She signs in to change how each one uses the calculator. (based on organisation settings) Sign in to an account with GOV.UK One Login, then change how the example organisations use the calculator.

Where to start

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