Distribution Calculator With Withdrawals: How It Works

This calculator works out the remaining balance of a retirement or investment account after a series of regular withdrawals, given an initial amount, a fixed annual return, and a withdrawal schedule. You enter the starting balance, the annual interest rate, the number of years, and the amount withdrawn each year (or each month), and it returns the ending balance after the final withdrawal. It uses the standard future value of an annuity formula, adjusted for the timing of withdrawals.

Formula

The calculator uses the future value of a series formula. The balance after n years is:

Ending Balance = P × (1 + r)^n − W × [((1 + r)^n − 1) / r]

Where:

• P = starting balance (in dollars, or any currency)
• r = annual interest rate (as a decimal, e.g., 5% = 0.05)
• n = number of years
• W = annual withdrawal amount (in the same currency as P)

The first term, P × (1 + r)^n, is the growth of the initial balance if left untouched. The second term subtracts the future value of a series of withdrawals, each made at the end of the year. This assumes withdrawals happen once per year, at the end of the year. For monthly withdrawals, you would adjust the rate and number of periods (see below).

Worked Example

Using the default values: P = $100,000, r = 5% (0.05), n = 20 years, W = $7,000 per year.

1. Calculate the growth factor: (1 + 0.05)^20 = 2.6532977
2. Future value of the initial balance: 100,000 × 2.6532977 = $265,329.77
3. Calculate the annuity factor: ((1.05)^20 − 1) / 0.05 = (2.6532977 − 1) / 0.05 = 33.065954
4. Future value of the withdrawals: 7,000 × 33.065954 = $231,461.68
5. Ending balance: 265,329.77 − 231,461.68 = $33,868.09

The calculator rounds to two decimal places, giving $33,868.09. This matches the result from the formula block.

When to Use This Calculator

This tool is useful for anyone planning to draw down a lump sum over a fixed period—retirees with a pension pot, someone funding a child’s education, or a trust that makes annual distributions. It helps answer: “If I start with a certain amount, earn a steady return, and withdraw a fixed amount each year, how much will be left at the end?�

It is also helpful in reverse: you can adjust the withdrawal amount to see how much you can take out without exhausting the fund too early. The calculator gives a clear picture of the trade-off between spending now and preserving capital for later.

How to Read the Result

The ending balance is the amount remaining after the last withdrawal. If it is positive, the fund survived the entire period. If it is zero, the withdrawals exactly depleted the balance. If it is negative, the fund ran out before the final year—meaning you would have needed a higher return, a lower withdrawal, or a longer period of growth.

Also look at the total withdrawn and total interest earned. The total interest is the difference between what you put in (starting balance) plus what you took out, and what you end with. A positive total interest means the account earned more than it lost to withdrawals. A negative number indicates the withdrawals exceeded the growth, eating into the principal.

Common Mistakes and Misconceptions

• Ignoring the timing of withdrawals: The formula assumes withdrawals occur at the end of each year. If you withdraw at the beginning of the year, the balance is slightly lower because the money doesn’t earn interest for that year. For beginning-of-year withdrawals, multiply the withdrawal term by (1 + r).
• Using nominal vs. effective rates: If interest is compounded monthly but you input an annual rate, the effective annual rate is higher. For monthly compounding, use the effective annual rate: (1 + monthly rate)^12 − 1.
• Forgetting inflation: This calculator uses nominal dollars. If inflation is 3% per year, a $7,000 withdrawal in year 20 buys far less than today. To model real purchasing power, subtract the inflation rate from the return rate.
• Assuming a constant return: Real investments fluctuate. This is a deterministic projection, not a guarantee. Running multiple scenarios with different rates gives a range of possible outcomes.

Adjusting for Monthly Withdrawals

If you withdraw monthly instead of yearly, you can still use this calculator by converting everything to monthly periods. Divide the annual return by 12 to get a monthly rate, multiply the number of years by 12 to get months, and divide the annual withdrawal by 12 to get the monthly withdrawal. The formula then gives the balance after the last monthly withdrawal. For example, with a 5% annual return, the monthly rate is 0.05/12 ≈ 0.004167. Over 20 years, that’s 240 months. A $7,000 annual withdrawal becomes $583.33 per month.

This adjustment works because the formula assumes equal periods and a constant rate. The result will be slightly different from the annual case because the timing of cash flows changes—monthly withdrawals start earlier and earn less interest.

Limitations of the Formula

This calculator assumes a fixed, constant annual return and a fixed withdrawal amount. Real-world portfolios have variable returns, and many retirees adjust withdrawals for inflation or market performance. The formula also assumes withdrawals happen at the exact end of each period, which is rarely true in practice. It does not account for taxes, fees, or the possibility of outliving the funds if you live longer than the period.

For a more realistic plan, use this calculator as a baseline, then stress-test with lower returns or higher withdrawals. Many financial planners use a “Monte Carlo� simulation to account for market volatility, but this simple formula gives a quick, understandable estimate.

Frequently Asked Questions

What if the ending balance is negative?

A negative balance means the withdrawals exceeded the growth, and the fund would run out before the final year. For example, if you start with $100,000, earn 5%, and withdraw $10,000 per year for 20 years, the ending balance is about −$33,000. That indicates the fund would be depleted around year 17. You would need to reduce the withdrawal, increase the return, or shorten the period.

Can I use this for a lump sum that I want to last forever?

Yes, but only if the withdrawal is less than the interest earned. If you withdraw exactly the annual interest, the principal remains intact forever. For a 5% return, that means withdrawing 5% of the balance each year. The formula would give a balance equal to the starting amount after any number of years, because the withdrawal equals the growth. Withdrawing more than the interest will eventually deplete the fund.

Does this calculator account for taxes?

No. The calculator ignores taxes on investment gains and on withdrawals. Depending on your jurisdiction and account type (e.g., traditional IRA vs. Roth IRA), taxes can significantly reduce the effective return. To approximate after-tax results, reduce the annual return by your marginal tax rate, or reduce the withdrawal amount by the tax owed.

What is the difference between this and a simple interest calculator?

A simple interest calculator only grows the initial principal without compounding, and it typically doesn’t handle regular withdrawals. This calculator uses compound interest, where the interest earned is added to the balance and earns more interest in subsequent years. That compounding effect is why the ending balance can be much higher than a simple interest projection.

How do I account for inflation?

Subtract the expected inflation rate from the annual return rate. For example, if you expect 5% nominal return and 3% inflation, use 2% as the rate in the calculator. This gives the ending balance in today’s purchasing power. Keep in mind that the withdrawal amount should also be adjusted for inflation if you want a constant real withdrawal.

Can I use this for a mortgage or loan payoff?

Yes, with a twist. For a loan, the starting balance is the loan amount, the annual return is the interest rate on the loan, and the withdrawal is the annual payment. The ending balance would be the remaining loan balance after the period. If you set the period to the loan term, the ending balance should be zero, which is how amortization works. This is essentially the same formula used for loan amortization.

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in p | Starting balance | $ | 100000 | 0
in r | Annual return | % | 5 | 0
in n | Years | years | 20 | 1
in w | Annual withdrawal | $ | 7000 | 0
out balance | Ending balance | $ | p * (1 + r/100)^n - w * (((1 + r/100)^n - 1) / (r/100)) | 2
out total_withdrawn | Total withdrawn | $ | w * n | 2
out total_interest | Total interest earned | $ | balance - p + w * n | 2