Transparency · Last reviewed: 16 June 2026
Methodology & sources
We believe a tax calculator should show its working. This page documents the exact figures, formulas and official sources behind every tool, plus what each one deliberately leaves out. If you find an error, please tell us — we update promptly and date every review.
Our principle: the tax mechanics (rates, caps, thresholds) are taken directly from official sources and applied precisely. Where a figure is a projection or an estimate, we say so. Nothing here is personal tax advice — see our disclaimer.
US — Self-employment tax (2026)
Used by the self-employment, DoorDash and Uber calculators.
| Figure | Value (2026) | Source |
|---|---|---|
| Net-earnings adjustment | × 92.35% | IRS Schedule SE |
| Social Security rate | 12.4% | SSA / IRS |
| Social Security wage base (cap) | $184,500 | SSA 2026 |
| Medicare rate | 2.9% (no cap) | IRS |
| Additional Medicare | +0.9% over $200k / $250k / $125k | IRS |
| Minimum earnings for SE tax | $400 | IRS |
| Standard mileage rate | 72.5¢ / mile | IRS (Notice, Jan 2026) |
Formula:
- Taxable base = net profit × 0.9235
- Social Security = min(base + W-2 SS wages, $184,500) portion × 12.4%
- Medicare = base × 2.9%, plus 0.9% on amounts over your filing threshold
- Deductible amount = half of the 15.3% portion (excludes the extra 0.9%)
- Quarterly estimate = total ÷ 4
What it excludes: federal income tax (shown separately on the gig calculators only), state taxes, the QBI deduction, and tax credits. The SE-tax figure itself is exact for the inputs you provide.
US — Federal income tax estimate (gig & state calculators)
The DoorDash, Uber and state calculators add an estimated federal income tax so the "set aside" number is realistic. It uses the 2026 standard deduction (single $16,100, married filing jointly $32,200, head of household $24,150) and the 2026 federal bracket schedule. The self-employment portion is always precise.
| Input / rule | How we handle it (2026) |
|---|---|
| Other household income | Optional field — your self-employment income is stacked on top, so it's taxed at the correct higher marginal brackets rather than from $0 |
| QBI (Section 199A) deduction | Optional 20% deduction on qualified business income (net profit less ½ SE tax), capped at 20% of taxable income |
| QBI phase-out threshold | $201,750 single / $403,500 MFJ — above this we warn the deduction may be limited (we don't model SSTB / wage limits) |
| State conformity to QBI | Not applied to state tax — most states don't follow the federal QBI deduction |
What it still excludes: tax credits, itemized deductions, retirement/health-insurance deductions, and (for the state layer) state-specific deductions and credits. Treat the income-tax figure as a well-informed estimate, not a filed return.
UK — IR35 status checker (2026/27)
This is an assessment, not a calculation. We weight your answers against the factors HMRC and the courts use, giving the three primary tests the most weight:
- Personal service / right of substitution — primary, highest weight
- Control (how, when, where) — primary, highest weight
- Mutuality of obligation — primary, highest weight
- Financial risk, being "part and parcel", exclusivity and equipment — secondary, lower weight
Each answer scores from −2 to +2 and is multiplied by the factor's weight. The overall ratio maps to a likely outside, borderline or likely inside result. The checker also accounts for the small-company exemption (private-sector client with two of: turnover ≤ £10.2m, balance sheet ≤ £5.1m, ≤ 50 employees), reflecting the April 2026 threshold change. This is indicative only — it is not a Status Determination Statement and has no legal standing.
UK — Inside vs outside IR35 take-home (2026/27, England)
| Figure | Value (2026/27) |
|---|---|
| Personal allowance | £12,570 (tapered over £100k) |
| Basic-rate limit | £50,270 |
| Additional-rate threshold | £125,140 |
| Dividend rates | 8.75% / 33.75% / 39.35% |
| Dividend allowance | £500 |
| Corporation tax | 19% / 25% with marginal relief (3/200) |
| Employer NI | 15% above £5,000 secondary threshold |
| Apprenticeship levy | 0.5% |
Outside IR35 models a limited company taking a £12,570 director's salary plus dividends from post-corporation-tax profit. Inside IR35 models deemed employment / umbrella PAYE, with employer's NI and the apprenticeship levy deducted from the assignment rate before income tax and employee NI.
What it excludes: Scottish income tax bands, student loan repayments, pension contributions, the employment allowance, VAT, and umbrella margins. It uses England/Wales/NI bands. The result is a like-for-like estimate to show the scale of the inside/outside gap, not a precise payslip.
How we keep figures current
We review rates at the start of each tax year — the US calendar year and the UK year from 6 April — and whenever HMRC or the IRS announces a mid-year change. Each calculator page is dated, and this methodology page carries the latest review date at the top. Some forward-year figures (for example, inflation-adjusted US brackets) can be released as projections and finalised later; where that's the case we label the estimate and update it on confirmation.
Official sources we rely on
- IRS — self-employment tax, Schedule SE, standard mileage rate, brackets
- SSA — Social Security wage base
- GOV.UK — IR35 / off-payroll working — status rules and small-company definition
- GOV.UK — Income Tax & dividend rates
We're committed to accuracy but can't guarantee every figure suits your circumstances. Always confirm against the official sources above or a qualified professional before acting. See our disclaimer.