How to Calculate Your RMD: The Divisor Table and the Aggregation Rules Nobody Mentions

Two numbers decide your required minimum distribution: the balance the IRS tells you to use, and the divisor for the age you reach this year. But the mistake that surprises people most comes after the math — taking the right total from the wrong account. A 401(k) dollar cannot be replaced by an IRA dollar, and one spouse's IRA cannot pay the other spouse's bill.

This guide works the calculation in order: balance, divisor, worked examples, then the aggregation map showing which accounts may be combined and which must stand alone.

Last updated: October 25, 2026.

The RMD Formula, in One Line

RMD = December 31 prior-year account balance ÷ the divisor for the age you reach in the distribution year.

The IRS states the same formula in Publication 590-B: figure the required minimum distribution by dividing the account balance at the close of business on December 31 of the preceding year by the applicable distribution period or life expectancy.

Three details do real work:

• The balance is last year's, not today's. A 2026 RMD starts from the value at the close of business on December 31, 2025.
• The age is the age you reach this year — on your birthday in 2026, not the age you were on December 31, 2025.
• The calculation is per account. Run the division separately for each account first; the aggregation rules then decide where the money may come from.

A custodian or plan administrator may calculate the amount, but the IRS holds the account owner ultimately responsible for taking the correct RMD.

In short: Last December 31 balance, divided by this year's age divisor, account by account. Then — and only then — check which totals the law lets you combine.

Step 1: The Balance That Counts

Start with the account's value at the close of business on December 31 of the preceding year. Contributions or distributions made after that date belong to the later year under Publication 590-B; they do not change the balance for the year being calculated.

Then make the adjustment almost nobody makes.

The money that was in no account on December 31

The IRA account balance is adjusted for outstanding rollovers — amounts that were in no account at the end of the preceding year. Publication 590-B gives the mechanics: for a rollover from a qualified plan or another IRA that was not in any account at the end of the preceding year, increase the account balance of the receiving IRA by the rollover amount, valued as of the date of receipt.

A trustee-to-trustee transfer caught between accounts at year-end follows the same receiving-account principle: it is not a distribution from the sending IRA, and the receiving IRA's balance and RMD are determined as they would be for a rollover. Money in transit is counted once, in the receiving account.

Example: $50,000 leaves a workplace plan on December 29, 2025 and lands in your IRA on January 6, 2026. It appears in no December 31 statement, but it belongs in the receiving IRA's adjusted balance. Skip it at age 75 and the RMD is understated by $50,000 ÷ 24.6 = $2,032.52.

Step 2: The Divisor — Uniform Lifetime Table, Ages 73–90

Most owners use the Uniform Lifetime Table (Table III in Publication 590-B, Appendix B). Find the age you reach in the distribution year; the number beside it is your divisor.

Age	Divisor	Age	Divisor
73	26.5	82	18.5
74	25.5	83	17.7
75	24.6	84	16.8
76	23.7	85	16.0
77	22.9	86	15.2
78	22.0	87	14.4
79	21.1	88	13.7
80	20.2	89	12.9
81	19.4	90	12.2

Source: IRS Publication 590-B (2025), Appendix B, Table III (Uniform Lifetime).

The divisor falls every year, so the required percentage rises even if the balance stands still: about 3.77% at 73 (divide by 26.5) and about 8.20% at 90 (divide by 12.2). Using last year's divisor is therefore a real shortfall, not a rounding error.

The one exception to Table III

If your spouse is the sole beneficiary of the account and is more than 10 years younger than you, do not use the table above. Use Table II, the Joint and Last Survivor Table, with the age you reach this year and the age your spouse reaches this year. The joint divisor is larger, so the RMD is smaller.

Publication 590-B's own example: a $100,000 balance, an owner who turns 75 in the distribution year, and a sole-beneficiary spouse who turns 64 — 11 years younger. The Table II divisor is 25.3, and the RMD is $100,000 ÷ 25.3 = $3,953. Both conditions must hold. A spouse who is 10 years younger or less, or a spouse who is one of several beneficiaries, leaves you on Table III.

Worked Example A: One Account, Start to Finish

Hypothetical. Tom reaches age 75 in 2026. His traditional IRA held $640,000 at the close of business on December 31, 2025. There were no outstanding rollovers.

1. Balance: $640,000 (December 31, 2025).

2. Age reached in 2026: 75 — divisor 24.6.

3. $640,000 ÷ 24.6 = $26,016.26.

Tom's 2026 RMD is $26,016.26. He may take more; he may not take less.

The Calculation as a Routine

Run every year in the same order:

1. List every account by type and owner. Your IRAs, your 403(b)s, each workplace plan, any inherited account — separate lines, no household totals yet.

2. Enter the balance that counts. December 31 of the preceding year, plus any outstanding rollover or transfer in transit, added once to the receiving account.

3. Fix the divisor. The age you reach in the distribution year, from Table III — or Table II if your sole beneficiary is a spouse more than 10 years younger.

4. Divide account by account. One line, one RMD figure, per account. Do not divide a combined balance unless the accounts share both an owner and an account type.

5. Group only where the map allows. Total your own IRAs together; total your 403(b)s together; leave every workplace plan, inherited account and spouse's account standing alone.

6. Withdraw and record. Note which account each dollar left and the date it left. Next year's calculation starts fresh from the new December 31 balances — this year's excess helps nobody next year.

The Aggregation Rules Nobody Mentions

Here is the part calculators skip: which calculated amounts may be pooled — satisfied by a withdrawal from a different account — and which may not.

Account type	Calculate…	The withdrawal may come from…
Your own traditional / SEP / SIMPLE IRAs	Each IRA separately	Any one or more of your own IRAs — the pooled total
Your 403(b) contracts	Each contract separately	Any one or more of your 403(b) contracts only
Each 401(k), 457(b) or other workplace plan	Each plan separately	That plan only
Your Roth IRA (as original owner)	No lifetime RMD	—
An inherited IRA you hold as beneficiary	Separately, under the beneficiary rules	Never pooled with your own IRAs
Your spouse's accounts	Your spouse calculates separately	Your spouse's accounts only

IRAs: calculate separately, withdraw together

The IRS requires a separate calculation for each IRA, because each RMD depends on that account's own December 31 balance. Once each figure exists, total them and take the total from any one or more of your own IRAs.

403(b)s: a pool of their own

Section 403(b) contracts work the same way inside their own lane: calculate each contract separately, then the total may be withdrawn from one or more of your 403(b) contracts. The lane is sealed. A 403(b) withdrawal does not satisfy an IRA RMD, and an IRA withdrawal does not satisfy a 403(b) RMD.

401(k)s and 457(b)s: no pooling at all

For 401(k) and 457(b) plans — and workplace defined-contribution plans generally — the IRS rule is the opposite: RMDs must be calculated and satisfied separately from each plan account. There is no household plan total. There is no making it up from a bigger IRA. Each plan's amount leaves that plan.

The still-working exception — current employer only

For a workplace plan (not an IRA), the first RMD is generally due April 1 after the later of the year you reach 73 or the year you retire — if the plan allows the delay. Two limits define it:

• Current employer's plan only. Working at 75 may defer that plan's RMD. It does nothing for a former employer's 401(k); that plan runs on the age rule.
• A 5% owner gets no delay. The first plan RMD is due April 1 after the year you reach 73, working or not.

IRAs have no still-working exception. The first IRA RMD is due April 1 after you reach 73 "even if you're still employed."

Worked Example B: Three IRAs, One Withdrawal

Hypothetical. Same age and divisor — 75 in 2026, divisor 24.6 — with the money spread across three IRAs. December 31, 2025 balances:

IRA	Dec 31, 2025 balance	÷ 24.6	This IRA's RMD
IRA 1	$210,000	÷ 24.6	$8,536.59
IRA 2	$95,000	÷ 24.6	$3,861.79
IRA 3	$40,000	÷ 24.6	$1,626.02

Calculated on the combined balance ($345,000 ÷ 24.6), the exact total obligation is $14,024.39. The three line items, each rounded to the cent, add to $14,024.40 — one cent of rounding. The safe instruction is the one on the worksheet: withdraw $14,024.40, the rounded-up total, and the requirement is covered to the cent.

Because these are all Tom's own IRAs, the entire $14,024.40 may come out of IRA 3 alone — the smallest account. Perfectly legal, and a common way to close small accounts one by one. It is lawful only because each line was first figured on its own balance.

Worked Example C: The 401(k) That Cannot Ride Along

Hypothetical. Same Tom, same three IRAs — plus a 401(k) from a former employer holding $180,000 on December 31, 2025.

$180,000 ÷ 24.6 = $7,317.07.

That $7,317.07 must be withdrawn from the 401(k) itself. Tom cannot add it to the IRA total and take $21,341.47 from his IRAs. If every dollar leaves the IRAs and nothing leaves the 401(k), he has still missed a $7,317.07 required distribution, because the IRS scores each workplace plan on its own. This is why the aggregation map — not the division — is the heart of the calculation.

The First-Year April 1 Option (and Its Price)

The first RMD gets one timing choice no later year gets: it may be taken by April 1 of the year after you reach 73 instead of by December 31 of the year itself.

Delaying does not move the second RMD, which remains due December 31 of that same following year. Take both in one calendar year and both are taxable income in that year — a bunching problem that can raise your bracket and, two years later, your Medicare premiums. The delay decision, and the double-RMD trap facing the 1953 birth year in 2026, are worked in full in our guide to the 2026 RMD deadline.

What a Shortfall Costs

Take less than required and the IRS imposes an excise tax of 25% of the amount not taken. Timely correction — withdrawing the missed amount within the correction window, generally two years — reduces the tax to 10%. A reasonable-error waiver can also be requested on Form 5329 when the shortfall came from a genuine mistake and you are fixing it.

Price Example C's trap: miss the $7,317.07 entirely and the excise tax is $1,829.27 at 25%, or $731.71 at 10% if timely corrected — and the distribution still has to come out. An excess distribution this year does not carry forward to next year, and an RMD amount cannot be rolled over.

If Your Custodian's Number Differs From Yours

Do not panic, and do not ignore it. Work the four inputs in order: the balance date (December 31 of the preceding year, not a current balance), any rollover or transfer that was in no account on that date, the table (Table III, or Table II for the younger-spouse exception), and the divisor for the age reached this year. Most disagreements live in one of those four.

Remember what a custodian's figure can and cannot see. It is built account by account; it cannot apply the aggregation map across institutions for you, and no custodian's IRA figure settles what a separate 401(k) owes. The IRS rule stands either way: the administrator may calculate, but the owner is ultimately responsible. If the difference survives the four checks, ask the custodian which balance and divisor it used — in writing — before you withdraw.

5 Calculation Mistakes That Cost Real Money

1. Using the wrong year's balance. The only balance in the formula is December 31 of the preceding year, close of business, adjusted for outstanding rollovers.

2. Using the age you were, not the age you reach. On a $640,000 balance, the age-74 divisor (25.5) gives $25,098.04 instead of the correct age-75 figure of $26,016.26 — a shortfall of $918.22, with an excise tax of $229.56 at 25%, or $91.82 at 10% if timely corrected.

3. Forgetting the rollover or transfer in transit. Money in no account on December 31 still counts — once, in the receiving account. Skipping $50,000 at age 75 understates the RMD by $2,032.52.

4. Taking the household total from one spouse's IRA. The IRS frames the rule around IRAs an individual holds as the IRA owner. Your total comes from your IRAs; your spouse's total comes from your spouse's IRAs. If one spouse takes both amounts from a single IRA, the other spouse has taken nothing.

5. Letting an inherited account ride along. The IRS states the boundary directly: you cannot total amounts from your own traditional IRAs with amounts from an inherited traditional IRA. Beneficiary accounts follow their own rules — worked in our inherited IRA rules guide.

Get the Free RMD Calculation Worksheet

One printable page: a balance line for every account, the divisor table for ages 73–90, and the aggregation map showing exactly which accounts may be combined — so the calculation and the withdrawal plan sit on the same sheet. Download the free worksheet (PDF), or have it emailed to you. Every worksheet we publish is collected on the Worksheets page.

Frequently Asked Questions

How do I calculate my RMD?

Divide the prior December 31 balance — adjusted for any outstanding rollover — by the divisor for the age you reach in the distribution year. Repeat for each account separately, then apply the aggregation rules to decide where withdrawals may come from.

Which December 31 balance do I use if I had a rollover in transit?

Add the amount once, to the receiving account's adjusted balance, valued as of the date of receipt (Publication 590-B). Money in no account on December 31 is still in the calculation.

Can I take my total IRA RMD from one IRA?

Yes. Calculate each of your own IRAs separately, total the amounts, and withdraw the total from any one or more of your own IRAs — not from a 403(b), a 401(k), or an inherited IRA.

Can I take my 401(k) RMD from my IRA instead?

No. Each workplace plan's RMD must be calculated and satisfied from that plan itself; extra IRA withdrawals do not count.

Can spouses combine their RMDs?

No. Each spouse's RMD is calculated on, and withdrawn from, that spouse's own accounts. There is no household total.

What happens if I take out less than my RMD?

The shortfall is subject to a 25% excise tax, reduced to 10% if timely corrected (generally within two years). The distribution is still owed, and a reasonable-error waiver may be requested on Form 5329.

Can I count an extra withdrawal this year toward next year's RMD?

No. Each year's RMD is figured fresh from the new December 31 balance and the new age divisor.

Sources

• IRS, Publication 590-B (2025), Distributions from Individual Retirement Arrangements (IRAs) — the calculation, the account-balance and outstanding-rollover rules, and Appendix B Tables II and III — https://www.irs.gov/publications/p590b
• IRS, Retirement Plan and IRA Required Minimum Distributions FAQs — calculation, aggregation for IRAs, 403(b)s and plans, responsibility, penalty and waiver — https://www.irs.gov/retirement-plans/retirement-plan-and-ira-required-minimum-distributions-faqs
• IRS, Retirement Topics — Required Minimum Distributions (RMDs) — the formula, table choice, deadlines, and the 25%/10% excise tax — https://www.irs.gov/retirement-plans/plan-participant-employee/retirement-topics-required-minimum-distributions-rmds
• IRS, RMD Comparison Chart (IRAs vs. Defined Contribution Plans) — first-RMD timing, the still-working and 5%-owner rules — https://www.irs.gov/retirement-plans/rmd-comparison-chart-iras-vs-defined-contribution-plans
• IRS, For Senior Taxpayers 2 (FAQs) — the own-IRA vs. inherited-IRA aggregation boundary — https://www.irs.gov/faqs/other/for-senior-taxpayers/for-senior-taxpayers-2

This article is educational information about how required minimum distributions are calculated, not personal tax advice. Account titling, plan documents, annuitized balances and beneficiary situations can change the calculation. Confirm your figures with your plan administrator or a qualified tax professional before you withdraw.