Retirement Calculator

How the Retirement Calculator works

Use this calculator when you want to compare one retirement scenario at a time and keep the active mode, ages, return, inflation, savings, target, and withdrawal assumptions visible. Use 401(k) for workplace contribution and match inputs, RMD for required distribution estimates, Annuity or Annuity Payout for product-style payout math, Investment or Savings for generic accumulation, and Future Value or Present Value for narrower time-value-of-money questions. Use SSA, IRS, DOL/EBSA, Investor.gov, SEC, FINRA, FCA, MoneyHelper, The Pensions Regulator, plan administrator, provider, prospectus, fee-disclosure, tax-authority, inflation-statistics, legal, or local regulator sources before making Social Security, retirement-plan, pension, tax, annuity, product, fee, inflation, legal, regulated-advice, or jurisdiction-specific claims.

The calculator first sets years to retirement as max(0, retirementAge - currentAge) and retirement years as max(0, lifeExpectancy - retirementAge). Retirement Need grows current income by incomeIncrease, multiplies it by retirementIncomePercent, subtracts otherMonthlyIncome * 12, floors the annual need at 0, discounts that annual need with a real annual return from investmentReturn and inflationRate, then projects currentSavings with a yearly income-savings loop using futureSavingsPercent. Savings Required grows currentSavings to retirement and solves an annual ordinary contribution needed to reach targetRetirementAmount; monthlySavingsNeeded is annualSavingsNeeded / 12, not a separate monthly-deposit solve. Withdrawal Amount rounds years to retirement into months, grows currentSavings monthly, adds monthlyContribution after each month's growth, adds annualContribution every 12th month, and estimates withdrawal capacity with a real monthly return. Money Last starts with amountHave, grows it with nominal monthly investmentReturn, subtracts the planned monthlyWithdrawal or remaining balance, counts whole months, and stops at 12000 months as a computational cap.

Retirement Calculator formula

This formula page covers the app's Retirement Calculator: four generic planning modes for retirement need, savings required, withdrawal capacity, and how long money may last. It uses the ages, income, contribution, return, inflation, savings, target, and withdrawal assumptions entered by the user. It does not calculate Social Security benefits, pension rights, annuity quotes, tax treatment, account limits, required distributions, market volatility, provider fees, guaranteed income, legal entitlements, or personalised retirement advice.

Step by step

1. Read the selected retirement question and the matching age, income, savings, contribution, return, inflation, target, amount-have, and withdrawal fields.
2. Compute Y as max(0, retirementAge - currentAge) and RY as max(0, lifeExpectancy - retirementAge). These clamps prevent negative planning periods.
3. In retirement-need mode, grow current income to retirement with IncRet = currentIncome * (1 + incomeIncrease / 100)^Y.
4. Apply the income-replacement percent and subtract other monthly income multiplied by 12, then floor the annual retirement need at 0.
5. Convert return and inflation into a real annual return with realR = (1 + R) / (1 + I) - 1.
6. Discount the level annual retirement need over RY retirement years. If the real return is near 0, use annual need times retirement years; otherwise use the annuity present-value factor.
7. Project retirement-need savings with a yearly loop: grow the previous balance by the investment return, then add that year's income times the future savings percent.
8. Set shortfall or surplus to projected savings at retirement minus required at retirement.
9. In savings-required mode, grow current savings to retirement, then solve the annual contribution needed to reach the target retirement amount.
10. If years to retirement is 0 or less, savings-required mode returns the target minus current savings, floored at 0. If the return rate is 0, it divides the remaining gap by years.
11. Display monthly savings needed as annual savings needed divided by 12. This is a display conversion, not a separate monthly-deposit formula.
12. In withdrawal-amount mode, convert years to retirement into rounded months, grow the balance monthly, add the monthly contribution after growth, and add the annual contribution every 12th month.
13. Use a real monthly return from investment return and inflation, then amortize the projected retirement balance across RY * 12 months to estimate monthly withdrawal capacity.
14. In money-last mode, start with the amount-have input, grow it by the nominal monthly investment return, subtract the smaller of planned withdrawal or current balance, and count whole months until the balance is depleted.
15. If monthly withdrawal is 0 or less, money-last mode returns the 12000-month cap. That cap is a safety branch, not a longevity or benefit forecast.
16. Round displayed currency outputs to two decimals after each mode's calculation and keep mode-specific unused outputs at 0.
17. Use official or primary sources before turning this generic planning math into Social Security, pension, retirement-plan, annuity, tax, investment-product, inflation-statistic, accounting, legal, lending, regulated advice, or jurisdiction-specific claims.

Worked example

Default examples across the four retirement modes

These examples use the app's current fixtures. They show how the formulas behave under fixed assumptions, not what any person needs to save or withdraw.

1. Retirement-need fixture: current age 35, retirement age 67, life expectancy 90, current income $85,000, income growth 3 percent, income replacement 75 percent, other income $1,200 per month, current savings $120,000, future savings 12 percent of income, return 6 percent, and inflation 3 percent.
2. The app models 32 years to retirement and 23 retirement years. The required amount at retirement is $2,485,143.11.
3. The same fixture projects savings at retirement of $2,093,029.74, so the displayed shortfall is $392,113.37.
4. Savings-required fixture: with current age 35, retirement age 65, current savings $75,000, a $1,000,000 target, and 6 percent return, the annual savings solve is $7,200.24.
5. The app displays monthly savings needed as $600.02 because it divides the annual savings solve by 12.
6. Withdrawal-capacity fixture: current age 50, retirement age 67, life expectancy 92, current savings $250,000, no monthly or annual contributions, 5 percent return, and 3 percent inflation project $583,879.71 at retirement.
7. That projected balance supports an estimated inflation-adjusted withdrawal capacity of $2,453.44 per month over 25 modeled retirement years.
8. Money-last fixture: amount-have $750,000, monthly withdrawal $4,000, and 5 percent return lasts 366 simulated months, displayed as 30.5 years.
9. These outputs are mechanical estimates from the entered assumptions. They are not Social Security estimates, pension valuations, annuity quotes, tax answers, investment recommendations, lender decisions, or personalised financial advice.

The Retirement Calculator is useful for comparing fixed-assumption retirement scenarios. The result can change sharply when ages, return, inflation, income growth, savings rate, target, or withdrawal amount change.

Assumptions and what this calculator ignores

Geographic scope: works globally. The math is currency-agnostic, so enter amounts in your own currency; local taxes, fees, and product rules are not included.

• Return, inflation, income growth, contribution, target, amount-have, withdrawal, age, and life-expectancy values are user-entered scenario assumptions. The calculator does not forecast markets, wages, inflation, benefits, tax law, plan rules, healthcare costs, fees, product terms, or lifespan.
• Different modes use different timing. Retirement Need projects yearly income-based saving; Savings Required solves an annual contribution and then divides by 12 for display; Withdrawal Amount uses monthly contributions after growth plus annual contributions every 12th month; Money Last uses a nominal monthly return and does not inflation-adjust the entered withdrawal.
• Package fixtures cover all four modes, and scoped internal independent comparator evidence covers savings-required annual outputs only. SSA sources are needed for Social Security claims; IRS and DOL/EBSA sources are needed for US retirement-plan rules; Investor.gov, SEC, FINRA, provider, prospectus, and fee-disclosure sources are needed for investment-product and fee claims; FCA, MoneyHelper, The Pensions Regulator, BLS, ONS, tax-authority, legal, and local regulator sources are needed before pension, annuity, inflation-statistic, tax, legal, regulated-advice, or jurisdiction-specific claims. Results are educational estimates, not financial, tax, legal, pension, benefits, investment, insurance, lending, regulated-product, or personalised advice.

What this formula does not include

• All return, inflation, income-growth, contribution, target, and withdrawal values are user-entered assumptions. The calculator does not forecast markets, inflation, wages, life expectancy, account performance, or future rules.
• Retirement-need mode uses annual income-replacement math and a real annual return. It does not model monthly spending, taxes, healthcare costs, benefits, sequence-of-return risk, changing spending, survivor needs, or irregular withdrawals.
• Projected savings in retirement-need mode grows current savings once per year and then adds that year's income times the future savings percent. It is not the same contribution timing as the withdrawal-amount mode.
• Savings-required mode solves an annual ordinary contribution. The monthly savings output is annualSavingsNeeded / 12, while the independent comparator solves monthly deposits directly with monthly compounding.
• Withdrawal-amount mode grows the balance monthly, adds monthly contributions after monthly growth, and adds annual contributions only on each 12th month. It then uses a real monthly return for withdrawal capacity.
• Money-last mode uses the nominal monthly return and a whole-month loop. It does not inflation-adjust the entered withdrawal and does not compare against the independent comparator as a strict oracle yet.
• The 12000-month cap is a computational guard for zero-withdrawal or long-lasting balances, not a guarantee that money lasts 1000 years.
• Scoped independent comparator checks currently pass 4 of 4 scoped savings-required annual-output fixtures. Retirement-need, withdrawal-capacity, and money-last modes need additional mapping before strict comparator validation.
• No Social Security benefit age, eligibility, replacement rate, or payment estimate is calculated. Those claims need SSA sources.
• No 401(k), IRA, pension, RMD, plan distribution, contribution limit, tax withholding, tax treatment, or retirement-account rule is calculated. Those claims need IRS, DOL/EBSA, plan administrator, or local authority sources.
• No annuity guarantee, insurer quote, pension-annuity shopping comparison, provider recommendation, surrender rule, or regulated retirement-income product claim is included. Those claims need FCA, MoneyHelper, The Pensions Regulator, SEC, FINRA, IRS, provider, or adviser sources as relevant.
• No investment product, fee, risk, diversification, prospectus, deposit-insurance, accounting, lending, legal, inflation-statistic, or jurisdiction-specific rule is included. Use Investor.gov, SEC, FINRA, BLS, ONS, product disclosures, lender disclosures, accounting standards, and local regulators before adding those claims.
• The result is an educational estimate from the entered assumptions, not financial, investment, tax, legal, pension, benefits, insurance, accounting, lending, regulated-product, or personalised advice.

Common mistakes to avoid

• Treating one retirement result as a forecast or complete plan. The output is only the result of the selected fixed assumptions.
• Comparing modes without noticing unused outputs or the annual-savings display convention. Several outputs stay at $0 or 0 when they do not apply, and the app solves annualSavingsNeeded before displaying monthlySavingsNeeded by dividing that annual amount by 12.
• Using the result as a Social Security estimate, pension valuation, annuity quote, tax calculation, product comparison, inflation forecast, legal answer, or personal recommendation.

Key terms

Retirement need

The modeled amount required at retirement for the entered income need. The app estimates it from income growth, replacement percent, other income, retirement years, return, and inflation.

Real return

A return assumption adjusted for inflation inside need and withdrawal formulas. The app uses real annual or monthly return when estimating required amount or withdrawal capacity.

Money-last duration

The whole-month count until the simulated balance is depleted. It uses the amount-have and monthly-withdrawal inputs, a nominal monthly return, and a 12000-month cap.

Frequently asked questions

Methodology, sources, and disclaimer

This calculator is an original four-mode retirement planner covering retirement need with real-return discounting, savings required, inflation-adjusted withdrawal capacity, and a money-last simulation, validated by deterministic fixtures and edge-case tests. It is not copied from a single source.

Fixtures pin each mode's formula path, including the real-rate conversion and the 12,000-month simulation cap. The result remains an educational estimate, not a pension projection or a retirement-income guarantee.

Formula version 2026.05.22-generic-retirement-planning-modes. The version marks the calculation logic and validation fixture set used for this estimate.

• SSA sources should be used before copy discusses Social Security benefit ages, eligibility, replacement rates, benefit estimates, or payment amounts.
• IRS and DOL/EBSA sources should be used before copy discusses US retirement-plan contributions, distributions, account rules, tax treatment, participant rights, employer plans, or savings guidance.
• Investor.gov, SEC, FINRA, product documents, prospectuses, fee disclosures, and provider materials should be used before copy frames fixed return assumptions as real investment returns, product performance, fees, risk, diversification, guarantees, or regulated investment guidance.
• FCA, MoneyHelper, The Pensions Regulator, BLS, ONS, local statistics agencies, tax authorities, accounting standards, lender disclosures, and relevant local regulators should be used before adding pension, annuity, inflation-statistic, tax, legal, accounting, lending, regulated advice, or jurisdiction-specific claims.

Results are educational estimates, not advice. Read the full disclaimer.

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