Methodology & Sources
The formulas, sources and review process behind every calculator on this site.
How This Site Is Produced
Smart Tool Hub is written and maintained by our small editorial team. Each calculator starts from a standard, published formula rather than a proprietary one, so that anyone can check our arithmetic against the original source. Before a tool goes live, we confirm that (a) the formula matches the published definition, (b) the code implements that formula, and (c) a worked example on the page produces the same result as the live tool.
Because money and health are topics that can affect real decisions, we treat them as Your Money or Your Life (YMYL) content: we name the underlying source, keep the assumptions visible, and avoid stating anything as personal advice. Tool pages carry a "Last reviewed" date, and the whole site is re-checked at least once a year or whenever a source changes (for example, new tax-year thresholds or updated health guidance).
Where Our Numbers Come From
We rely on primary sources from government agencies, standards bodies and peer-reviewed literature. The main references by topic are:
| Topic | Primary sources |
|---|---|
| Mortgage, loan, refinance, credit card | Consumer Financial Protection Bureau (CFPB) loan and mortgage guidance; standard amortisation mathematics |
| Estimated tax, take-home pay | US Internal Revenue Service (IRS) publications and current-year brackets; HMRC (UK); Canada Revenue Agency (CRA); Australian Taxation Office (ATO); Inland Revenue (NZ); OECD tax database |
| Compound interest, retirement, savings | US Securities and Exchange Commission (Investor.gov); Federal Reserve interest-rate data |
| BMI, BMR, calorie targets | US CDC and National Institutes of Health (NIH) for BMI and weight categories; World Health Organization (WHO) classification; Mifflin–St Jeor (1990) and Harris–Benedict (1919) equations for basal metabolic rate |
| Unit conversion | National Institute of Standards and Technology (NIST) Handbook 44; BIPM SI Brochure (exact definitions of SI units) |
| Dates and age | Gregorian calendar rules and ISO 8601 date conventions |
Formulas at a Glance
- Loan / mortgage payment: M = P × i × (1+i)n / ((1+i)n − 1), where P is principal, i the periodic rate and n the number of payments.
- Compound interest: A = P(1 + r/n)nt plus the future value of any regular deposits.
- BMI: metric kg / m2; imperial 703 × lb / in2.
- BMR (Mifflin–St Jeor): 10×kg + 6.25×cm − 5×age + s (s = +5 male, −161 female); TDEE = BMR × activity factor.
- Percentage change: (new − old) / old × 100.
Every tool page repeats its own formula and a worked example, so the calculation is never hidden behind the interface.
Corrections and Updates
If you believe a formula, figure or explanation is wrong or out of date, please tell us through the Contact page or email chenjinhua326@gmail.com. We investigate every report and, where a change is warranted, update the tool and move the "Last reviewed" date forward.
Nothing on this site is financial, tax or medical advice. Calculated results are estimates for general information, and you should confirm important decisions with a qualified professional.
Last updated: October 5, 2026 · Contact: chenjinhua326@gmail.com
本站内容如何产出
Smart Tool Hub 由我们的小型编辑团队撰写与维护。每个计算器都以公开发表的标准公式为起点，而非自创公式，因此任何人都可以拿原始出处来核对我们的算式。工具上线前，我们会确认三件事：(a) 公式与官方定义一致；(b) 代码正确实现了该公式；(c) 页面上的算例结果与实时工具一致。
由于金钱与健康会直接影响真实决策，我们把这类内容视为 YMYL（关系金钱与生命）内容：标明依据来源、让假设条件可见，并且绝不将其表述为个人建议。工具页都带有"最近复核"日期；全站至少每年复核一次，来源发生变化时（例如新的税年阈值或更新的健康指南）也会即时复核。
数据来源
我们依据政府机构、标准组织与同行评审文献等一手来源。按主题划分的主要参考如下：
| 主题 | 主要来源 |
|---|---|
| 房贷、贷款、再融资、信用卡 | 美国消费者金融保护局（CFPB）贷款与房贷指南；标准摊还数学 |
| 预估税、到手工资 | 美国国税局（IRS）出版物与当年税率表；英国 HMRC；加拿大 CRA；澳大利亚 ATO；新西兰 Inland Revenue；OECD 税务数据库 |
| 复利、退休、储蓄 | 美国证券交易委员会（Investor.gov）；美联储利率数据 |
| BMI、BMR、热量目标 | 美国 CDC 与国立卫生研究院（NIH）的 BMI 与体重分级；世界卫生组织（WHO）分类；Mifflin–St Jeor（1990）与 Harris–Benedict（1919）基础代谢公式 |
| 单位换算 | 美国国家标准与技术研究院（NIST）Handbook 44；BIPM 国际单位制手册（SI 单位的精确定义） |
| 日期与年龄 | 公历规则与 ISO 8601 日期规范 |
核心公式一览
- 贷款 / 房贷月供：M = P × i × (1+i)n / ((1+i)n − 1)，其中 P 为本金，i 为每期利率，n 为期数。
- 复利：A = P(1 + r/n)nt，并叠加定期存款的未来价值。
- BMI：公制 kg / m2；英制 703 × lb / in2。
- BMR（Mifflin–St Jeor）：10×kg + 6.25×cm − 5×年龄 + s（s：男 +5，女 −161）；TDEE = BMR × 活动系数。
- 百分比变化：(新值 − 旧值) / 旧值 × 100。
每个工具页都会重复自己的公式与算例，计算过程不会藏在界面背后。
纠错与更新
如果你认为某个公式、数字或说明有误或已过时，请通过联系页面或邮件 chenjinhua326@gmail.com 告诉我们。我们会核查每一条反馈，确有需要时更新工具并把"最近复核"日期后移。
本站任何内容都不构成财务、税务或医疗建议。计算结果仅为一般性估算，重要决策请咨询合格的专业人士。
最后更新：2026 年 10 月 5 日 · 联系方式：chenjinhua326@gmail.com