About This Site

Why I made it

A lot of us feel a little uneasy about planning for the future. I felt that way too. And yet a "neutral, free tool" that lets you think things through with your own numbers in three minutes turns out to be surprisingly hard to find. Paid financial-planner consultations, bank simulators, Excel templates — each has its place, but they feel a bit off for the simple goal of poking around and taking home one insight.

This site is meant to fill that "poke around and take home one insight" gap. Feel free to play with it however you like.

Principles (three of them)

• No financial products for sale: there are no referral links to bank accounts, brokerage accounts, or apps. No financial affiliate links either. I do run general ads to cover the cost of keeping the site going, but I have set things up to exclude the financial category (banks, brokerages, FX, loans, crypto) from ad delivery.
• No sign-up, free: I don't ask for your email address. Nothing is stored on a server.
• The formulas are public: the Assumptions page lays out every formula, assumed value, and source.

Who runs it

NinjaTech (SinobuTech) — Sinobu, an independent creator, runs this on their own. If you'd like to know a bit more, feel free to take a look at the main NinjaTech site as well.

Who this tool is — and isn't — for

Probably a good fit if you are

• A university student or someone new to working life wondering, "I'd like to start investing or saving, but how much should I start with?"
• Someone who wants to compare how decisions like marriage, buying a home, or having children might affect your assets
• Someone who finds financial jargon a little intimidating and just wants a rough sense of the numbers first

Probably not a good fit if you are

• Already building a detailed plan with a financial planner or tax accountant (a dedicated tool will likely serve you better)
• Looking to design the drawdown of your retirement assets precisely (another tool will be more dependable)
• Aiming to run business simulations for a company or sole proprietorship

Even if none of that fits, you're welcome to play with it anyway.

Disclaimer

The results shown on this site are only a rough guide. They do not guarantee your future assets. Outcomes can shift considerably depending on tax rules, the pension system, market conditions, and your own circumstances. Before any important decision, it's worth consulting a public institution or a qualified professional (a financial planner, tax accountant, and so on) for greater peace of mind. The operator cannot be held responsible for any damages arising from use of this site, so please understand this in advance.

Updates and improvements

Phase 1 started by shipping the bare minimum as an MVP — "move the sliders and the chart moves" — and from there I've added features bit by bit while reflecting on feedback.

Recent improvements (v1.2, May 2026)

• Automatic child-rearing costs — On top of education costs (daycare fees, tuition, enrollment fees), age-based child-rearing costs (food, clothing, allowance, communication, etc.) are now added to household spending automatically. Rough figures: about ¥35,000/mo for ages 0–2, ¥45,000/mo for ages 6–11, and ¥80,000/mo for ages 18–21.
• Child age-gap slider — With two or more children, you can now set the year gap from the eldest, so birth costs, university enrollment fees, and education costs are spread realistically over time (previously it assumed a triplets model where everyone was born the same year).
• Part-time job ON/OFF toggle — For people who don't work part-time (relying only on family support, or going straight to work after vocational school, etc.). Turning it OFF treats the pre-employment period as having no income.
• Target amount shown at F.Age — Beyond the "age at which money stops being a worry" (Financial Independence Age), the tool now also shows the target asset amount needed to reach it (annual spending × 25).
• Improved shareable URL — The hash now stays in the URL bar, so you can restore a scenario by re-sharing or reloading. Prototype-pollution protection was also added.
• Keyboard support — Life events can now be toggled ON/OFF with Tab + Enter/Space (WCAG 2.1.1 compliant).
• Real-time car and home summaries — Loan repayment and total payment now update the moment you change a property price or purchase cost. An automatic link also keeps the down payment from exceeding the property price.
• Dynamic hint text — When you change the "age of becoming a full-time employee," the hint "part-time period is X years" now updates at the same time.
• Separating severance pay from pension — Fixed a bug where severance pay was mixed into the "total pension" label. Pension is now shown as pension, and severance as severance.

What I'd like to do next (Phase 2)

• Scenario comparison — A feature to line up and compare married/not, home-purchase/not, and so on
• Reflecting NISA / iDeCo tax deductions — The January 2027 iDeCo expansion (¥62,000/mo for company employees without a corporate pension, extended to age 70) and the new NISA limits (¥3.6M/yr, ¥18M lifetime)
• Dual-income household model — Partner income and combined take-home pay for couples
• Mortgage tax deduction (0.7% of the year-end balance, up to 13 years, ¥210,000/yr)
• Free university tuition (large families) — Tuition and enrollment fees free up to the national cap for households with three or more dependents (starting FY2025)
• Macroeconomic slide — Reflecting the decline in the real purchasing power of public pensions (switchable between a present-value basis and a future-value basis)
• A Portuguese version (tied to the operator's Cruzamento brand, for Japanese-Brazilian readers)

A detailed list of systems and assumptions not yet reflected is in Assumptions §7.

If you have feedback like "this part is confusing" or "I'd love this feature," I'd be glad to hear from you via Contact. Let's make it better together!