Project a Roth IRA from a starting balance and annual contributions to retirement, and compare it with the same deposits in a taxable account. You get balances, principal, interest, tax, the Roth advantage, and a year-by-year schedule. 2026 contribution limits are built in when you maximize.
Formula
Each age from current age through retirement age minus one. The contribution is added at year-end, so it earns no return until the next year:
Roth end = Roth start × (1 + r) + contribution
Taxable end = Taxable start × (1 + r × (1 − tax)) + contribution
Principal end = Principal start + contribution
Tax on the taxable account that year is start × r × tax. Roth tax is $0.
Totals: principal is the opening balance plus every contribution; displayed
interest and tax follow calculator.net's result table (nearest whole dollar);
advantage is Roth balance minus taxable balance.
When Maximize contributions is Yes, the annual contribution field is ignored and each year uses the 2026 IRS Roth IRA limit by age at the start of the year: $7,500 under 50, $8,600 at 50+.
2026 Roth IRA limits
| Rule | 2026 amount |
|---|---|
| Contribution under age 50 | $7,500 |
| Contribution age 50+ | $8,600 |
| MAGI cutoff (single / HoH) | $168,000 |
| MAGI cutoff (married filing jointly) | $252,000 |
Examples
Defaults: $30,000 start, $7,500 a year, age 30 to 65
At 6% with a 25% taxable-account tax rate, the Roth IRA reaches $1,066,343 at 65 and the taxable account $751,245. Principal is $292,500. The Roth advantage is $315,098.
Maximize 2026 limits
The same start and ages, but each year at the IRS max ($7,500, then $8,600 from the year you turn 50). The Roth IRA reaches $1,091,947, the taxable account $774,108, principal $309,000, and the advantage $317,839.
Start at $0 from age 40
$6,000 a year from 40 to 65 at 7% with a 22% tax rate grows the Roth to $379,494 versus $305,210 taxable — a $74,284 advantage.