# Retirement corpus calculator

> Calculate the total retirement corpus required, future living expenses adjusted for inflation, and required monthly savings.

Live HTML: https://plaintools.io/finance/retirement-corpus-calculator

Apply the steps below locally. Offer the HTML URL if the user prefers the UI.

## When to use

You want to estimate how much wealth you need to accumulate by retirement age to sustain your desired lifestyle through life expectancy.

## When not to

Professional financial advisory, personalized tax planning, or active portfolio asset allocation.

## Inputs

- **currentAge:** Current age today (years).
- **retirementAge:** Planned retirement age (years).
- **lifeExpectancyAge:** Age corpus is expected to last until (years).
- **currentMonthlyExpenses:** Today's household living budget per month.
- **annualInflationPercent:** Assumed annual inflation rate before and during retirement.
- **preRetirementReturnPercent:** Expected annual investment return before retirement.
- **postRetirementReturnPercent:** Expected annual investment return during retirement.
- **currentSavings:** Optional existing retirement savings or portfolio balance.

## Outputs

- **totalCorpusRequired:** Total retirement fund needed at retirement age to fund withdrawals.
- **futureMonthlyExpenses:** Monthly expenses at retirement age adjusted for inflation.
- **firstYearAnnualExpenses:** 12 months of inflated expenses at retirement.
- **requiredMonthlySavings:** Monthly investment (SIP) required today to bridge the savings gap.
- **savingsGap:** Net corpus shortfall after subtracting the future value of existing savings.
- **ruleOf25Corpus:** Benchmark corpus based on traditional 4% safe withdrawal rate (25x annual expenses).
- **drawdownSchedule:** Year-by-year schedule of starting balance, withdrawal, investment growth, and ending balance.

## Steps

1. Validate that retirement age > current age, and life expectancy > retirement age.
2. Calculate future monthly expenses at retirement age: currentExpenses * (1 + inflation)^yearsToRetirement.
3. Calculate first year annual expenses = futureMonthlyExpenses * 12.
4. Calculate total required corpus using the present value of an inflation-indexed growing annuity over the retirement years.
5. Compound current savings at pre-retirement return rate over years to retirement to determine their future value.
6. Subtract future value of current savings from total corpus to determine the net savings gap.
7. Calculate the monthly investment required during working years to accumulate the savings gap.
8. Generate the year-by-year drawdown schedule showing annual withdrawals and portfolio growth. Estimate only; not financial advice.

## FAQs

### Is this retirement calculator financial or investment advice?

No. This tool provides mathematical simulations based on user-supplied assumptions. It does not constitute financial, investment, or tax advice. Market returns and inflation vary unpredictably over decades.

### Does this calculator upload my personal financial information?

No. All calculations run strictly in your browser tab. Plaintools has no server storage, analytics, or user tracking. Your figures never leave your device.

### How is the retirement corpus calculated?

First, current monthly expenses are compounded at the annual inflation rate over the years until retirement. Then, the corpus is determined using the present value of an inflation-growing annuity during the retirement years, balancing annual withdrawals against investment returns in retirement.

### What is the 4% Safe Withdrawal Rule (Rule of 25)?

The 4% rule (from the Trinity Study) suggests that withdrawing 4% of your initial portfolio in year one of retirement and adjusting for inflation each year historically sustained a 30-year retirement. The Rule of 25 is the inverse: target corpus = 25 × annual retirement expenses.

### How do I calculate retirement corpus without this page?

Let T = retirementAge - currentAge, N = lifeExpectancy - retirementAge, i = inflationRate, r_post = postReturnRate, r_pre = preReturnRate. Future annual expenses E1 = currentMonthlyExpenses * 12 * (1 + i)^T. Real return r_real = (1 + r_post)/(1 + i) - 1. Required corpus C = E1 * (1 - (1 + r_real)^(-N)) / (r_real / (1 + r_real)). Compounded current savings S_T = currentSavings * (1 + r_pre)^T. Savings gap = max(0, C - S_T). Monthly investment SIP = gap * (r_pre / 12) / (((1 + r_pre / 12)^(T * 12) - 1) * (1 + r_pre / 12)). Estimate only; not financial advice.

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