Roth IRA Calculator Explained

The account the IRS stops watching once you fund it

A Roth IRA is the after-tax retirement account that sits under §408A of the Internal Revenue Code. You put in money that has already been taxed, it grows tax-free for the rest of your life, and qualified withdrawals — age 59½ AND a five-year hold satisfied — come out federally tax-free in retirement. The Roth IRA calculator projects the balance you will have at retirement from six inputs: current age, the age you plan to retire, your planned annual contribution, an expected annual return, your tax filing status, and your modified adjusted gross income. This article walks the 2025 contribution limits, the MAGI phase-out that decides whether you can contribute directly, the future-value-of-annuity formula behind the projection, the five-year rule, the backdoor Roth route, and the withdrawal mechanics that decide when (and how) the money comes back out.

All dollar figures in this article are 2025 IRS limits taken from Notice 2024-80 (November 2024 cost-of-living release) and Publication 590-A, which is the authoritative source for the worksheet maths the calculator implements.

What a Roth IRA actually is

Senator William Roth of Delaware attached the provision that became IRC §408A to the Taxpayer Relief Act of 1997, and the Roth IRA opened for business on January 1, 1998. The pitch was a deliberate inversion of the Traditional IRA: instead of deducting contributions now and paying tax on the whole pot at withdrawal, you give up the front-end deduction in exchange for a complete federal-tax exemption on the back end. Everything you contribute is post-tax basis you can pull back at any time. Everything the account earns inside the wrapper is tax-free if you wait until age 59½ and have held a Roth for at least five tax years.

Two structural features sit underneath that headline. The IRS treats Roth IRAs as never having lifetime required minimum distributions — you are not forced to take money out at age 73 the way Traditional IRAs require, so the balance can compound for as long as you live. And the basis-first ordering rule under §408A treats your own contributions as the first dollars withdrawn, so a Roth doubles as a deep emergency fund: pull the basis if you must, leave the earnings to compound. The Roth IRA calculator models the contribution and growth side; the withdrawal mechanics are tax law and are summarised lower down.

The 2025 contribution limit

The base limit for 2025 is $7,000 if you are under 50 and $8,000 if you are 50 or older. The extra $1,000 is the §219(b)(5)(B) age-50 catch-up, which is not indexed for inflation and has sat at $1,000 since 2008. The limit is a per-person aggregate across all your Traditional and Roth IRAs combined — you can split between them but the total cannot exceed the cap. Spouses each get their own limit and a non-working spouse can fund a "spousal IRA" against the working spouse's earned income under §219(c).

The limit is also capped at your "taxable compensation" for the year. A retired person living on dividends and Social Security has no earned income and cannot contribute. A teenager with $2,400 of summer-job wages can contribute up to $2,400, not the full $7,000. Compensation includes wages, salary, tips, bonuses, commissions, self-employment income, and taxable alimony (for divorce decrees executed before 2019). It does not include investment income, rental income, or pension benefits.

The MAGI phase-out by filing status

Roth eligibility depends on your modified adjusted gross income — the IRS's way of letting middle earners fund Roths while shutting out high earners. The 2025 phase-out ranges (Pub 590-A Table 2-1) are:

• Single / Head of Household: $150,000 – $165,000
• Married Filing Jointly: $236,000 – $246,000
• Married Filing Separately (lived with spouse any time during the year): $0 – $10,000

Below the lower threshold you get the full base limit. Above the upper threshold you cannot contribute directly to a Roth — at all. Inside the band the limit reduces pro-rata: the calculator implements IRS Pub 590-A Worksheet 2-2 line for line — compute the excess MAGI over the lower threshold, divide by the phase range, multiply by the base limit, subtract from the base limit, then round the result up to the nearest $10. There is a $200 floor while you are still partially eligible: any positive reduced limit under $200 becomes $200, dropping to zero only when MAGI hits the upper bound. The brutal Married-Filing-Separately band — $0 to $10,000 — exists to stop high-earning couples from gaming the limit by splitting their return.

MAGI is AGI from line 11 of Form 1040 plus a handful of add-backs: student-loan interest, the foreign earned-income exclusion, foreign housing exclusion, exclusion of bond interest from US savings bonds used for education, exclusion of employer-provided adoption benefits, and any Traditional IRA deduction. For most filers MAGI equals AGI. If your income is in the phase-out band, recompute MAGI carefully before contributing — guessing wrong and over-contributing gets you a 6 % annual excise tax under §4973 until you remove the excess.

The future-value maths

Once the calculator has your MAGI-adjusted contribution limit, it applies the ordinary-annuity future-value formula:

FV = C × ((1 + r)ⁿ − 1) / r

where C is your effective annual contribution (capped at the MAGI-adjusted limit), r is your expected annual return as a decimal, and n is years to retirement. The formula treats contributions as end-of-year deposits, which slightly understates the result versus a beginning-of-year assumption — the difference is about one year of extra growth on the whole portfolio, typically a few percent at retirement. The choice mirrors Vanguard's Roth IRA calculator and Excel's FV() with type=0, which makes the figures cross-checkable.

The "expected return" input is where the projection lives or dies. Long-run US large-cap equity returns are roughly 10 % nominal and 7 % real (Aswath Damodaran's annual NYU dataset is the standard source). The calculator defaults to 7 %, which is conservative against the S&P 500 historical figure and closer to a real-terms answer. For a 60/40 stock-bond mix use 5–6 %; for a bond- heavy conservative allocation use 3–4 %. Many planners run the same projection at 5 %, 7 %, and 9 % to bound the answer, then plan contributions against the middle scenario.

Worked example

A 35-year-old single filer earning $80,000 contributes $7,000 per year to a Roth IRA for 30 years (to age 65) at a 7 % expected return. MAGI is well below the $150,000 lower phase-out threshold so the full $7,000 base limit applies. Running the future-value formula:

FV = 7,000 × ((1.07)³⁰ − 1) / 0.07
FV = 7,000 × (7.6123 − 1) / 0.07
FV = 7,000 × 94.4608
FV = $661,225

The entire $661,225 is federally tax-free in retirement. Total contributed — the basis — is 7,000 × 30 = $210,000, so tax-free investment growth is $451,225. Applying the Bengen 4 % safe- withdrawal rule (4 % of the starting balance, then inflation- adjusted) gives roughly $26,449 of annual tax-free retirement income, or $2,204 per month, before Social Security and any other pensions. Try it in the Roth IRA calculator — change the return assumption to 5 % and the balance drops to roughly $465,300; raise it to 9 % and it climbs above $953,500.

Factors that change your Roth outcome

Time horizon

The single biggest lever. A $7,000 annual contribution at 7 % over 30 years grows to $661,225; over 35 years it grows to $968,068 — a 46 % bigger balance from a 17 % longer time horizon. The compounding tail is always the biggest single chunk of the final balance, which is why starting in your 20s rather than your 40s changes retirement outcomes more than almost any other variable.

The MAGI-adjusted limit

If you are in the phase-out band, your effective contribution is smaller than the base limit and the projection shrinks proportionally. A single filer with $158,000 MAGI is roughly in the middle of the $150,000–$165,000 band and gets a reduced limit of about $3,270. The projection runs on $3,270 a year, not $7,000 — a roughly 53 % cut to the tax-free balance at retirement. If your MAGI bounces above and below the band from year to year, your contribution will too.

Expected return

A 2-percentage-point swing in expected return — from 5 % to 7 % — gives roughly 42 % more balance at year 30. From 7 % to 9 %, another 44 %. Compounding rewards high return assumptions exponentially, which is also why pension scammers love quoting 12 % returns. Use a conservative number you actually expect a real portfolio to deliver net of fund fees, and treat the headline figure as an upper envelope.

Sequence-of-returns risk

The future-value formula assumes one steady return rate. Real markets deliver lumpy returns, and a bad sequence near retirement can wreck a portfolio even when the long-run average is on target. A 2008-style 40 % drawdown in your last working year on a $660,000 balance costs you $264,000 you no longer have the time to earn back. The 4 % rule is itself partly an answer to sequence risk — Bengen picked it because it held up across the worst historical 30-year windows. The calculator does not model sequence risk explicitly; treat the projection as a smoothed-average answer, not a guarantee.

Fees

Expense ratios are a tax on returns and they compound the wrong way. A 0.04 % index fund at Vanguard or Fidelity leaves the math nearly alone. A 0.85 % actively managed fund eats roughly 29 % of compound growth over 30 years ((1.0085)³⁰ − 1 ≈ 0.290). When you control the Roth IRA outside an employer plan, fee discipline is the easiest single decision you can make.

The backdoor Roth and the IRS pro-rata rule

If your MAGI is above $165,000 single or $246,000 married-joint, direct Roth contributions are not allowed — but the conversion side of the rules has no income cap. The "backdoor Roth" exploits this gap: contribute (non-deductible) to a Traditional IRA, then convert the same dollars to Roth before they earn meaningful interest. The conversion is reported on Form 8606 and produces no taxable income because the basis equals the conversion amount.

The trap is the IRS pro-rata rule under §408(d)(2): the conversion is taxed proportionally on the pre-tax fraction of all your IRA balances combined. If you have $50,000 in a rollover Traditional IRA from an old 401(k) plus the new $7,000 non-deductible contribution, the IRS treats your aggregate IRA basis as 7,000 / 57,000 = 12.3 %. Converting the $7,000 means only 12.3 % of it ($861) is treated as basis and the other 87.7 % ($6,139) is ordinary income. The backdoor only works cleanly when your only IRA money is the fresh non-deductible contribution. The standard workaround is to roll the pre-tax IRA balance into a 401(k) plan (which is not counted in the pro-rata calculation) before executing the conversion. Get a CPA involved — this is one of the easier ways to file an incorrect 1040.

The five-year rules

There are two separate five-year rules and they get conflated all the time. The first applies to qualified withdrawals of earnings: for the earnings portion of any withdrawal to come out federally tax-free, your first Roth IRA contribution to any Roth account must have happened at least five tax years ago. The clock starts on January 1 of the tax year of that first contribution — a Roth contribution made on April 15, 2025 for tax year 2024 backdates the clock to January 1, 2024. Open a Roth with $100 in your 20s if you can, even if you do not fund it seriously yet — the clock is cheap to start.

The second five-year rule applies to Roth conversions: each conversion has its own five-year holding period before the converted amount can be withdrawn penalty-free if you are under 59½. Once you hit 59½, the conversion five-year rule disappears entirely. It rarely binds for older savers and is a major consideration for the FIRE crowd doing aggressive conversion ladders in their 40s. The two clocks run independently.

Withdrawing from a Roth IRA

Roth withdrawals follow the ordering rules in §408A: contributions first, then conversions (oldest first), then earnings. Contributions come out at any time, at any age, federally tax- and penalty-free — the IRS treats them as having been taxed already. Conversion principal also comes out tax-free, but is subject to the 10 % early- withdrawal penalty if within five years of the conversion and you are under 59½. Earnings are the only layer where the qualified- withdrawal rules really bite — to avoid both tax and penalty on earnings you generally need to be at least 59½ and to have held a Roth IRA for five tax years.

Several earnings exceptions exist even if the qualified-withdrawal test is not met: first-home purchase up to $10,000 lifetime, qualified higher-education expenses, birth or adoption costs up to $5,000, terminal illness, disability, and death. See IRS Pub 590-B for the comprehensive list and the documentation each exception requires.

Roth IRA vs other retirement accounts

The Roth IRA does not replace the other US retirement vehicles — it complements them, and the optimal ordering depends on your tax bracket and employer match. The conventional priority order for someone with access to all of them: contribute to a 401(k) up to the full employer match (the match is a 50–100 % return on those dollars in year one), then max the Roth IRA ($7,000 / $8,000), then top up the 401(k) the rest of the way ($23,500 §402(g) cap), then any after-tax 401(k) bucket your plan offers (the "mega backdoor" Roth route).

A Traditional IRA shares the contribution limit pool but flips the tax treatment — deduction now, ordinary-income tax on withdrawal — and is itself subject to MAGI deductibility limits if you or your spouse is covered by a workplace plan. A 403(b) is the public-sector and nonprofit cousin of the 401(k), with the same §402(g) limit and an extra 15-year service catch-up at some plans. RMDs from the Traditional accounts start at age 73 (born 1951–1959) or 75 (born 1960 or later) under SECURE 2.0 — see the RMD calculator for the Uniform Lifetime Table maths. The Roth IRA stays untouched until you decide to draw it.

Common mistakes

Over-contributing through ignorance of the limit. Excess Roth contributions carry a 6 % annual excise tax under §4973 until you remove them. The cleanest fix is a "corrective distribution" by the tax filing deadline (with extensions) of the excess plus its earnings; otherwise the 6 % keeps applying each year. Custodians do not always catch over-contributions in real time — track them yourself.

Conflating the two five-year rules. Earnings require the five-year rule plus 59½; conversions have their own independent five-year clock under 59½ only. Both rules together confuse a lot of people approaching early retirement.

Triggering pro-rata on a backdoor Roth. Any pre-tax IRA balance — including a rollover IRA from an old 401(k) — turns the backdoor into unexpected taxable income. Roll the pre-tax balance back into a 401(k) plan before converting, or model the tax bill in advance.

When to seek professional advice

The Roth IRA calculator handles the contribution maths and the future-value projection at a single steady return — enough for most people most of the time. Talk to a fee-only fiduciary planner or a CPA when (a) you are inside the MAGI phase-out band and considering a backdoor Roth while holding pre-tax IRA balances, (b) you are coordinating Roth conversions with anticipated low-income years in early retirement, (c) you are weighing the basis-first withdrawal property for a major non-retirement expense, or (d) state tax treatment of Roth withdrawals matters (most states follow the federal exemption, but the details vary). The numbers from the Roth IRA calculator are a starting point for the conversation, not the end of it. This article is informational and is not personalised tax or investment advice.

Frequently asked questions

See the FAQ section on the Roth IRA calculator page for the 2025 contribution limits, the MAGI phase-out by filing status, the backdoor Roth, the RMD-exempt status, the basis-first withdrawal ordering rule, and the Roth IRA vs Roth 401(k) decision.

Related calculators

• Roth IRA Calculator — project tax-free retirement balance with 2025 MAGI phase-out applied.
• IRA Calculator — compare Traditional vs Roth IRA outcomes under your own tax assumptions.
• 401(k) Calculator — project a 401(k) balance with 2025 IRS limits and employer match.
• 403(b) Calculator — public-sector and nonprofit retirement projection.
• RMD Calculator — required minimum distributions for Traditional accounts using the IRS Uniform Lifetime Table.
• Compound Interest Calculator — future value of a lump sum plus contributions at any compounding frequency.
• Annuity Calculator — solve for future value, present value, or payment using time-value-of-money formulas.