Finance Online Tools

What Is Compound Interest? Use the Rule of 72 to Estimate Doubling Time Learn what compound interest is, how it differs from simple interest, and how to use the Rule of 72 to estimate how long money takes to double, with examples and long-term saving insights. How Much Do You Need for FIRE? The 4% Rule and Annual Spending × 25 Learn the basics of FIRE (financial independence, early retirement): the annual-spending × 25 formula and the 4% rule behind it, the four types (Fat/Lean/Coast/Barista), and key risks, with concrete examples. How to Choose a Mortgage: Variable vs. Fixed Rates, Repayment, Deduction A clear guide to choosing a mortgage: variable vs. fixed rates, equal-payment vs. equal-principal methods, safe debt-to-income guidelines, prepayment, and the tax deduction. Japan Retirement Lump Sum Tax Basics: Deduction & Net Guide Understand how a Japanese retirement lump sum (taishokukin) is taxed: the service-based deduction, half-taxation, separate taxation, your net amount, and when to file a return. Crypto Tax Basics in Japan: Miscellaneous Income and Filing Explained A beginner-friendly guide to taxes on crypto profits in Japan: how miscellaneous income and progressive aggregate taxation work, when gains are realized, why calculation is hard, how it differs from stocks and FX, and when you must file. How Much Do You Need to Live Off Dividends? Yield Math and Taxes Learn how to plan the money needed to live off dividends: back-calculating the required investment from target dividend ÷ yield, the 20.315% tax and NISA tax-free benefit, dividend-cut risk, and a realistic high-yield strategy with examples. Gross vs. Net Salary in Japan: What Gets Deducted and How Much Understand the difference between gross annual income and take-home pay in Japan: income tax, resident tax, and social insurance deductions, the 75–85% net-pay rule, a quick reference table, and the basics of deductions. New NISA vs iDeCo: Differences, Which to Prioritize, and Using Both Compare new NISA and iDeCo by tax exemption, withdrawal freedom, deductions, and limits. Learn which to prioritize and how to use both, explained by situation. Annual, Monthly, Hourly Pay Conversion: Methods, Work Hours, Gross vs. Net Learn how to convert annual salary into monthly and hourly pay from the basics: the work-hour assumptions such as 160 hours a month, the difference between gross and net, how to handle bonus-inclusive salaries, and what to watch when comparing job offers. Freelance Taxes and Tax Returns Explained: Income Tax, Resident Tax, Insurance, Pension, Blue Return A beginner-friendly guide to taxes and tax returns for freelancers and sole proprietors: income tax, resident tax, national health insurance, national pension, and enterprise tax, the difference between blue and white returns, deductible expenses, the 650,000-yen blue return deduction, and an overview of consumption tax (invoice system). Japanese Car Tax (Shubetsu-wari) Basics: Rates by Engine Size, Kei Cars, Monthly Proration A beginner-friendly guide to Japan's annual car tax (shubetsu-wari): rough rates by engine displacement, how it differs from the kei (light) car tax, why the April 1 owner is charged, monthly proration, the green-car reduction and the 13-year surcharge, and how to pay. Are Point Rewards Worth It? Effective Price and % Reward vs % Discount From the meaning of a reward rate, to calculating the effective price including points, the difference between an X% reward and an X% discount, stacking points, the true value of one point, and tips for telling whether a deal is really worth it. How Effective Is Mortgage Prepayment? Term-Shortening vs. Payment-Reduction Learn how much interest mortgage prepayment can save, from the basics: the difference between term-shortening and payment-reduction types, how interest is reduced, why earlier is more effective, balancing with cash reserves, the trade-off with loan insurance and tax deductions, and points to check first. Gift Tax Basics: The 1.1M Yen Exemption, Tax Rates, and Settlement Options A beginner-friendly guide to gift tax in Japan: the annual 1.1 million yen exemption under calendar-year taxation, how the tax and the general vs. special rates work, the inheritance-time settlement system, education and housing fund exemptions, the link to inheritance tax, and when you must file. How to Calculate Overtime Pay: Hourly Rate, Premium Rates, and Fixed Overtime Learn how overtime pay is calculated from the ground up: how to find the hourly rate (base wage divided by average monthly scheduled hours), the premium rates of 25% for overtime, 25% for late-night, and 35% for holiday work, how fixed (deemed) overtime works, the over-60-hours premium, and worked examples. The Time Value of Money: Present Value, Future Value, and Discount Rate Learn the time value of money from the ground up: why money today is worth more than the same amount later, future value with compounding, present value via discounting, and how to apply it to investing and saving. This article is general information, not investment advice. How Resident Tax Works: Income & Per-Capita Levy, Prior-Year Basis, Deductions Learn how Japanese resident tax works from the basics: the income-based levy (about 10% of taxable income) and the per-capita levy, why it is charged the year after the income is earned, deductions, special vs. ordinary collection, and its link to furusato nozei. Interest Rate Basics: Annual Rate, Simple vs Compound, APR, and the Rule of 72 A beginner-friendly guide to interest rate basics: how annual, monthly, and daily rates relate, the difference between simple and compound interest, APR vs nominal rate, the Rule of 72 for estimating doubling time, what interest means for deposits and loans, and fixed vs variable rates. What Is Depreciation? Straight-Line vs Declining Balance, Useful Life, and Small-Asset Rules A beginner-friendly guide to depreciation: spreading the cost of fixed assets over their useful life, the difference between straight-line and declining-balance methods, acquisition cost, useful life and residual value, the small-asset special rule, and how sole proprietors handle it on a tax return. What Is the Break-Even Point? Fixed, Variable Costs and How to Find It Learn the meaning of the break-even point and how to calculate it: how to split fixed and variable costs, contribution margin and margin ratio, the formula break-even sales = fixed costs / margin ratio, the break-even ratio, the effect of price cuts and cost reductions, and use in business planning. Household Budgeting Basics: Take-Home Pay, Fixed vs Variable Costs, Ideal Spending Ratios, and Savings Rate A beginner-friendly guide to household budgeting: grasp your take-home pay, separate fixed and variable costs, learn ideal spending ratios for housing and food, understand your savings rate and pay-yourself-first saving, cut fixed costs, and build habits that last. What Is the Invoice System? Qualified Invoices, Registration, and Tax Credits A beginner-friendly guide to Japan's invoice system: what a qualified invoice is, how registered businesses work, the link to the purchase tax credit, the impact on taxable and tax-exempt businesses, required invoice items, and what freelancers and sole proprietors should know. Planning Savings From a Goal: How Much to Save Monthly, With Compounding Learn how to work backward from "how much by when" to the monthly amount you need to save: a simple division estimate, calculating with a return (compounding), how to set return assumptions, and tips for realistic goals. General information, not investment advice. Finance Basics: Principal, Yield, Compounding, Risk, and Diversification A beginner-friendly guide to the financial terms you should know before saving or investing: principal, yield, compounding, risk and return, diversification, index investing, dollar-cost averaging, and liquidity. This article is general information, not investment advice. What Is ROI? The Formula, Worked Examples, Annualizing, and ROAS vs. Yield Learn what ROI (Return On Investment) is from the ground up: the meaning of the formula profit ÷ investment × 100, worked examples, how to annualize it over a holding period, how it differs from ROAS and yield, and how to use it in investment decisions and its limits. Why Is Your Bonus Take-Home So Small? Japan Bonus Tax Explained Learn why a Japanese bonus (shoyo) net amount is lower than gross: social insurance (health, pension, employment) and income tax withholding, plus a gross-to-net guide. Taxes on Stock Profits: The 20.315% Rate and Account Types Explained A beginner-friendly guide to taxes on stock and fund profits in Japan: the 20.315% rate breakdown, account types, loss offsetting and carryover, and tax-free NISA investing. iDeCo Tax Benefits and Drawbacks Explained, With Limits by Occupation A clear guide to iDeCo tax savings (full deduction, tax-free gains, payout deductions), drawbacks like no withdrawals until age 60, and contribution limits by occupation. New NISA Guide and the Power of Compounding｜30,000 Yen a Month for 20 Years Learn the basics of Japan's new NISA (accumulation and growth frames, 18 million yen lifetime tax-free limit) and why compounding grows your money, with concrete examples and risk notes. How the Furusato Nozei Limit Is Decided: System, Income & Family Caps A beginner-friendly guide to how the Furusato Nozei deduction limit is set—built around about 20% of your resident tax income levy—plus a 2026 table by income and family, who sees a lower limit after the 2026 tax reform, One-Stop vs. tax return, and key cautions.