CRA T4127, 122nd and 123rd editions, 2026

Every deduction, with its receipt.

Takehome computes Canadian payroll deductions from the CRA's own formulas: federal and provincial tax, CPP, CPP2 and EI for twelve provinces and territories plus work outside Canada. One Rust engine answers in this tab, in the API and in the packages, and it shows every factor it used.

Run a paycheque See the proof

PDOC forms matched, default: 8,905 / 9,002
With the PDOC rounding arm: 8,987 / 9,002
Floats in the engine's money path: 0

01 The stub

Run a paycheque. Read every line.

The calculation below runs in this tab: the Rust engine compiled to WebAssembly. No salary figure leaves the browser.

Earnings statement

Federal tax

Provincial tax

CPP

CPP2

Total deductions

Net pay

Employer pays

Not withheld from the employee: the employer's own CPP and EI on this pay.

Employer CPP

Employer CPP2

Employer EI

Employer cost (gross + premiums)

No salary figure leaves the browser.

The working

Every factor the engine used, with its value and the T4127 section it comes from. Links open the CRA edition that answered this pay date.

Show factors that are zero for this pay

Factor	What it is	CRA source
A	Annual taxable income	T4127 Ch. 4, Step 1
P	The number of pay periods in the year	T4127 Ch. 4, Step 1
C	Canada (or Quebec) Pension Plan contributions	T4127 Ch. 6
C2	Second additional Canada (or Quebec) Pension Plan contributions	T4127 Ch. 6
EI	Employment insurance premiums	T4127 Ch. 7
F5	Deductions for Canada Pension Plan additional contributions	T4127 Ch. 4, Step 1
F5A	CPP additional-contribution deduction	T4127 Ch. 4, Step 1
BPAF	Federal Basic Personal Amount	T4127 Ch. 2, Table 8.2
TC	Total claim amount reported on federal Form TD1	T4127 Ch. 2
CEA	Canada Employment Amount	T4127 Ch. 8, Table 8.2
R	Federal tax rate	T4127 Ch. 8, Table 8.1
K	Federal constant; the tax overcharged when applying the higher federal rates to A	T4127 Ch. 8, Table 8.1
K1	Federal non-refundable personal tax credit (lowest federal tax rate × TC)	T4127 Ch. 4, Step 2
K2	Federal tax credit for base CPP contributions and EI premiums	T4127 Ch. 4, Step 2
K4	Federal non-refundable tax credit calculated using the Canada employment amount	T4127 Ch. 4, Step 2
T3	Annual basic federal tax	T4127 Ch. 4, Step 2
T1	Annual federal tax deduction	T4127 Ch. 4, Step 3
TCP	Total claim amount reported on the provincial or territorial Form TD1	T4127 Ch. 2
V	Provincial or territorial tax rate	T4127 Ch. 8, Table 8.1
KP	Provincial or territorial constant	T4127 Ch. 8, Table 8.1
K1P	Provincial or territorial non-refundable personal tax credit (lowest provincial rate × TCP)	T4127 Ch. 4, Step 5
K2P	Provincial or territorial tax credit for base CPP contributions and EI premiums	T4127 Ch. 4, Step 5
K4P	Territorial non-refundable tax credit calculated using the provincial or territorial Canada employment amount	T4127 Ch. 4, Step 5
K5P	Provincial supplemental non-refundable tax credit (lowest provincial tax rate)	T4127 Ch. 4, Step 5
T4	Annual basic provincial or territorial tax	T4127 Ch. 4, Step 4
V1	Provincial surtax calculated on the basic provincial tax (Ontario only)	T4127 Ch. 4, Step 5
V2	Ontario Health Premium calculated on taxable income	T4127 Ch. 4, Step 5
S	Provincial tax reduction (Ontario and British Columbia)	T4127 Ch. 4, Step 5
Y	Additional Ontario tax-reduction amount based on the number of eligible dependants	T4127 Ch. 4, Step 5
T2	Annual provincial or territorial tax deduction (except Quebec)	T4127 Ch. 4, Step 5
T	Estimated federal and provincial or territorial tax deductions	T4127 Ch. 4, Step 6

02 The proof

Checked against the CRA's own calculator, to the cent.

8,982 boundary forms were entered into the CRA Payroll Deductions Online Calculator (PDOC) for the July 2026 edition, plus 20 Ontario forms from January. Every PDOC line is compared with the engine on every test run. Nothing is exempted from the count.

Default arm, t4127

8,905/9,002

98.92% of forms match on all seven lines

rounding_compat: pdoc

8,987/9,002

99.83% with the CPP line in binary64, as inferred from PDOC's outputs

Before 22 October 2026

8,838/9,002

164 one-cent disagreements, cause unnamed

Three named rules close 149 of the 164 one-cent gaps

K2 is two credits, not one. T4127 writes the CPP and EI credit as (0.14 x CPP base) + (0.14 x EI base), and the T1 return computes them on separate lines. T4127's text does not say where to round; PDOC rounds each to the cent before adding. The engine now does too, in the default arm.
Ontario surtax is two lines.(0.20 x (T4 - 5,818)) + (0.36 x (T4 - 7,446)), each rounded. Default arm.
PDOC's CPP line matches binary floating point, inferred from its outputs: (500.00 - 350.00) x 0.0595 is exactly 8.925 in decimal, which T4127 rounds to 8.93. In IEEE-754 binary64 it is 8.924999999999999, and PDOC shows 8.92. That one rule explains all 82 CPP-line gaps. The default arm keeps decimal arithmetic for CPP; rounding_compat: pdoc reproduces PDOC with integer-only binary64 emulation, so no float enters the money path.

The default arm follows T4127 plus two PDOC-matched roundings T4127's text does not specify: K2/K2P credits and Ontario surtax lines are rounded separately. The rules were chosen by inspecting the full corpus; 15 cases remain unexplained. The PDOC corpus was captured from live PDOC, last capture 2026-09-15.

PDOC agreement by jurisdiction, July 2026 queue (8,982 compared forms)
Jurisdiction	Forms	Match, t4127	Match, pdoc	Status
Alberta	732	726	732	All match
British Columbia	912	905	911	1 off by 1 cent
Manitoba	678	668	676	2 off by 1 cent
New Brunswick	614	608	614	All match
Newfoundland and Labrador	860	852	858	2 off by 1 cent
Nova Scotia	670	662	668	2 off by 1 cent
Northwest Territories	612	606	612	All match
Nunavut	602	594	600	2 off by 1 cent
Ontario	1,100	1,090	1,096	4 off by 1 cent
Prince Edward Island	734	727	733	1 off by 1 cent
Saskatchewan	552	545	551	1 off by 1 cent
Yukon	488	480	488	All match
Outside Canada	428	422	428	All match

The 15 forms still one cent apart, listed

Each is a period tax line where the engine's annual tax divided by the pay periods lands within a fraction of a cent of a half-cent. No published rounding rule we tested reproduces PDOC on these, so they count against both rates. Full requests and outputs are in the conformance record.

Jurisdiction	P	Gross	Claim	Line	Engine	PDOC
BC	240	106.55	1	Federal	3.43	3.44
MB	24	1958.33	0	Federal	245.85	245.84
MB	24	1958.33	1	Federal	149.88	149.87
NL	53	842.97	0	Federal	105.65	105.66
NL	240	930.59	1	Provincial	127.96	127.97
NS	22	2817.78	0	Provincial	314.91	314.90
NS	240	258.29	1	Provincial	24.49	24.50
NU	240	1077.00	0	Provincial	86.68	86.69
NU	240	310.82	1	Provincial	10.52	10.53
ON	10	5852.29	1	Provincial	285.28	285.29
ON	13	2769.24	0	Federal	344.39	344.38
ON	13	447.54	0	Federal	43.99	43.98
ON	13	447.55	0	Federal	43.99	43.98
PE	240	445.37	1	Provincial	51.24	51.25
SK	12	4544.33	1	Provincial	264.48	264.47

Also measured: Ontario January corpus 20/20; PDOC bonus corpus 19/20 (its own class, not in the rate). Latest PDOC capture 2026-09-15. Quebec is not supported and is not in any count.

03 How it works

One engine, every runtime.

The same Rust function answers in the browser, in the API and in the packages. Each response names the rule set and the engine build hash, so a payroll team can pin exactly what it tested.

CRA T4127 tables. January and July 2026 editions, archived as CSV with SHA-256.
Rule data. Effective-dated JSON per edition; July overlays January.
takehome-core (Rust). Exact decimal money, one named rounding per step, no clock, network or IO.
Every runtime. WebAssembly in the browser and embed widget, the Cloudflare Worker API, and npm and PyPI packages (takehome-ca, not yet published).
Conformance gate. 9,002 PDOC forms checked on every test run.

Hard problems, solved in code: exact decimal money (ADR-001); rounding that follows T4127 step by step, with a PDOC arm (ADR-003, ADR-007); effective-date versioning, so a pay date picks its edition; metering that fails closed, so a meter outage refuses the request instead of serving it unmetered (ADR-005).

Read the API docs Full conformance record