Calculator Methodology and Limitations

Purpose and scope

These tools calculate deterministic planning scenarios from the inputs shown. They do not retrieve bank balances, market prices or official benefit records. A displayed number is not a recommendation, probability of success or guarantee. Worked examples are illustrative calculations rather than market forecasts.

Growth and deposit timing

Monthly growth tools divide a nominal annual percentage by 12 and add deposits at month end. Future value is P(1+i)^n + C((1+i)^n−1)/i. At a zero rate the formula becomes P+Cn. The interest calculator separately supports simple interest and a selected compound frequency.

Annual percentage yield and nominal annual rate are not identical. Some other tools use effective monthly conversion instead of annual rate divided by 12. Differences in deposit timing, rate convention and rounding can explain small discrepancies. Currency outputs are rounded for display while calculations retain numeric precision.

Retirement targets and income

The main retirement model converts annual returns to real rates using (1+r)/(1+inflation)−1, then divides by 12. It adjusts contributions annually relative to inflation. The savings target is the present value of the monthly spending gap over the chosen retirement horizon. It assumes a zero target ending balance, outside income beginning at retirement and constant real outside income.

The extra monthly saving calculation uses the same contribution-growth path as the projected balance. Scenario cards compare savings balances only; changing retirement age in the full form is necessary to recalculate retirement need. The future-money view converts retirement-date figures using the entered inflation factor.

Income and 401(k) withdrawal tools solve a level nominal monthly annuity payment. The withdrawal-duration tool instead raises withdrawals annually by the entered rate and simulates up to 1,200 months. A balance still positive at the cap is labeled as lasting more than 100 years.

Fees, returns and tax approximations

Fund tools subtract the annual expense percentage from gross return. Brokerage projections also subtract the entered annual tax drag. These are percentage-point approximations, not daily fee accrual or a tax-lot model. Returns already net of costs should not have the same costs deducted again.

ROI and holding-period return use simple start/end values. CAGR assumes no intervening external cash flows. Portfolio projections use weighted constant asset returns and do not simulate correlation, rebalancing, volatility or changing allocations. The S&P 500 tool is not a historical backtest.

U.S. accounts and benefits

Account tools use stored 2026 planning limits. The 401(k) tool updates age-based eligibility as years pass; Roth 401(k), 403(b) and IRA projections hold the contribution cap associated with the entered current age constant. Future statutory increases, combined plan ceilings, income eligibility and compensation tests are not comprehensively enforced.

Social Security worker benefits are adjusted from a user-entered full-retirement-age amount, not calculated from lifetime earnings. Break-even is an undiscounted cumulative-payment comparison. Taxable Social Security is an inclusion estimate rather than a final tax bill. Pension, FERS and military tools implement only the simplified formulas described on their pages.

Country profiles

Country selection changes currency labels and stored pension context. It does not perform foreign-exchange conversion or fetch current laws. A contribution-year checkpoint cannot establish entitlement. Users must confirm birth-cohort, residence, employment and transition rules with the authority linked on the relevant profile.

Country profile content is a starting reference, not a certification that every law is current or every exception is covered. Public pension amounts are supplied by the user. Model delayed or fixed nominal benefits separately if the main model’s constant-real-income assumption does not fit.

Validation, sources and corrections

Forms validate numeric ranges and required relationships, including retirement after current age and asset weights totaling 100%. Results are cleared when inputs are invalid. A successful calculation confirms only that supported input checks passed, not that the assumptions are suitable.

Official sources are linked on the relevant pages. The 2026 contribution values were checked against the IRS announcement. Social Security inputs should be confirmed through SSA. See the corrections policy and contact page to report a reproducible issue.