Frequently Asked Questions

MoneyMath is an independent suite of personal finance calculators — 17 of them, covering mortgages, loans, savings, investing, retirement, taxes, currency, and inflation. Every page shows the formula, walks through a worked example, and lists the things it does not model. There are no accounts, no lead-generation forms, and no affiliate recommendations baked into the math.

Yes, free. No. The calculators run entirely in your browser — numbers you type are never sent to a server. We do not have a sign-up form, a newsletter, or any way to collect your personal information. The site is supported by display advertising (Google AdSense).

The math is exact for the model each calculator uses. The model itself is always a simplification of real-world finance. Mortgage rates depend on individual credit history; tax bands change every year; investment returns vary; lender stress tests differ by bank. Every calculator page lists what it does not include in a "What this calculator does NOT model" section. Treat the numbers as planning estimates, not authoritative quotes.

MoneyMath is run from Gibraltar, which sits at the intersection of UK, Spanish, and (in some cases) US tax systems. The Salary calculator covers Gibraltar (ABS), the UK (PAYE), Spain (IRPF), and the United States (federal). The Tax Bracket and ISA vs Pension calculators are UK-specific because those tax wrappers don't have direct equivalents elsewhere. Most other tools (mortgage, loan, compound interest, etc.) are universally applicable — they just default to GBP because that's our local currency.

Gibraltar uses sterling (Gibraltar pound, at parity with GBP), and the UK is the largest natural audience for the kind of content we publish. If you're working in EUR, USD, or another currency, the math is identical — the £ symbol is essentially a label. The Salary calculator switches automatically to EUR for Spain or USD for the US.

The Salary and Tax Bracket calculators use approximate 2025/26 tax bands. Tax rules change every year in every country — these calculators are educational, not authoritative. For a current, binding figure, consult your country's official tax authority calculator (HMRC, Spain's Agencia Tributaria, US IRS, Gibraltar ITO) or a qualified accountant.

The Currency Converter uses the open-source Frankfurter API, which serves the European Central Bank's daily reference rates. The ECB publishes once per working day, around 16:00 CET. These are mid-market rates — banks, brokers, and apps will charge a spread of 0.1% to 8% on top depending on the provider. Do not use this calculator for trading decisions; use a real FX terminal.

No. Calculator inputs are processed entirely in your browser by JavaScript and are not sent to any server we control. The Net Worth Tracker uses localStorage to remember your assets, liabilities, and snapshots across visits, but that data lives only in your browser — clearing site data wipes it. See our Privacy Policy for the full disclosure.

Marginal rate is the rate on your next pound earned — the rate of the highest bracket your income reaches. Effective rate is the total tax you pay divided by your total income, which is always lower than the marginal rate (except for very low earners). When people talk about being "in the 40% tax bracket," they're referring to their marginal rate. Their actual effective rate is usually much lower because the first £12,570 is tax-free and the next slice is taxed at only 20%. See the Tax Bracket Calculator for a per-band breakdown.

The 4% rule comes from a 1998 Trinity University study which found that a US-based retiree withdrawing 4% of their portfolio in year one, then increasing that amount for inflation each year afterwards, would have lasted 30 years in roughly 95-98% of historical rolling periods. It is not a fixed-percentage rule (you don't withdraw 4% each year — you withdraw 4% in year one and grow that pound amount with inflation), it is not a guarantee (5% historical failure means 5%), and modern researchers often recommend 3-3.5% for safer global portfolios or longer horizons. See the Retirement Drawdown Calculator for an honest treatment.

Mathematically, compare your mortgage rate to your after-tax expected investment return. If your mortgage is at 5.5% and your investments return 7% pre-tax (~5.6% after basic-rate UK tax on dividends), it's close to a wash — and the certainty of paying down the mortgage often wins on risk-adjusted terms. If your mortgage is at 3% and investments could return 7%, investing wins comfortably. Behavioural factors matter too: paying down a mortgage is psychologically rewarding and removes a major monthly bill. Most people's optimal answer is "some of both" — capture employer pension match first, then split additional savings between mortgage overpayments and investments based on rate and risk tolerance.

In the UK, capture any employer pension match first — it's free money you can't replicate elsewhere. Beyond that, the dominant variable is your current marginal tax rate versus your expected retirement marginal rate. If higher now (40-45% currently, expecting 20% in retirement), pension wins, often by 30-50%. If lower now than later, ISA wins. If you're under 40 and saving for a first home, the Lifetime ISA's 25% government bonus is hard to beat for amounts up to £4,000/year. See the ISA vs Pension Calculator for the per-scenario math.

Three to six months of essential monthly expenses — not income, expenses. If your job is secure and you have other safety nets (family, dependable side income, redundancy package), three months may be enough. If you're self-employed, in a specialised field with long job-search timelines, or the sole earner for a family, lean toward 9-12 months. Build the first month (or £1,000, whichever is larger) before anything else, then pay off high-interest debt, then capture employer pension match, then build the full fund. See the Emergency Fund Calculator for the itemised math.

For context only: in the UK in 2024-25, the median household net worth is roughly £300,000, the 75th percentile is around £700,000, the 90th is £1.3 million. These numbers are dominated by home equity and pensions; median liquid net worth is far lower. But comparing yourself to percentiles is the wrong frame — the right question is whether your number is trending up year over year, given your saving rate and investment returns. Net worth is a personal stock, not a competitive scoreboard.

Three reasons. First, Google AdSense renders cleanly against light backgrounds and historically had issues with dark themes. Second, calculator pages have a lot of text content with formulas and tables — light themes are easier on the eyes for long-form reading. Third, the warm parchment palette is intentional and consistent with the editorial aesthetic. We may add a dark mode toggle later, but it's low priority.

Email us via the address on the About page. We genuinely respond to bug reports and consider every calculator suggestion. If you spot a math error, please include the inputs you used and the output you saw — that makes diagnosis instant.