A trust fund lets you set aside money now so that a child, grandchild, spouse, or charity receives support over time — but the numbers behind it are easy to underestimate. The balance does not just sit there: it grows from investments, shrinks from the payouts you make to beneficiaries, and is reduced every year by the trustee you pay to manage it. On very large trusts, a separate generation-skipping transfer tax can take a sizable slice before a grandchild ever sees a dollar.
This trust fund calculator projects all of those moving parts at once. Enter the principal, the return you expect, the percentage you plan to distribute each year, and the trustee fee. The engine then walks the balance forward year by year, subtracting each year's payout and fee and adding the year's growth, so you can see whether the trust will survive for the term you intend — or whether it will run dry.
How to Use
- Enter the Initial Trust Fund — the principal you (or a grantor) place into the trust at funding. This is the base amount every other figure grows out of.
- Set the Expected Annual Return. A balanced stock-and-bond portfolio historically averages roughly 6%–8% over long horizons; use 5%–6% if you want a conservative stress test.
- Choose the Annual Distribution Rate — the share of the balance paid to beneficiaries each year. A common sustainable starting point is 4%, the same draw-down rule of thumb used in retirement planning.
- Add the Trustee Fee. Corporate trustees typically charge 0.5%–2.0% of assets per year; an individual trustee may charge a flat or hourly fee instead.
- Set the Projection Years to how long you expect the trust to last, such as until a beneficiary reaches a certain age or completes college.
- Adjust the GST Exemption Threshold only for very large trusts. The 2025 lifetime generation-skipping transfer exemption is $13.61 million per person; the calculator flags any principal above that and applies the 40% top federal rate to the excess.
The result card breaks out the first year's growth, payout, and fee, then shows the projected balance at the end of the term, the total dollars paid to beneficiaries, and any estimated GST tax exposure.
How the Projection Works
Each year the trust follows the same simple chain: the balance grows at your expected return, then the beneficiary distribution and the trustee fee are withdrawn from that balance. In math form:
Balance(next year) = Balance × (1 + (Return% − Distribution% − Fee%))
Suppose the trust starts at $500,000, returns 7%, distributes 4%, and pays a 1% trustee fee. The net effect is growth of 7% − 4% − 1% = 2% per year. Year one produces $35,000 of investment growth, $20,000 of beneficiary payouts, and a $5,000 trustee fee — leaving the trust with about $510,000. Repeating that chain for 20 years grows the balance to roughly $742,974, while beneficiaries collect about $485,947 in total payouts along the way.
The key insight is the gap between the return and the combined payout plus fee. If the return exactly equals the distribution plus fee, the trust stays flat forever. If the return is lower, the trust slowly shrinks and can eventually hit zero — the classic "trust fund runs out" scenario. Slide the distribution rate upward and watch the projected balance turn downward.
The Generation-Skipping Transfer (GST) Tax
Most people only think about estate tax, but a second federal tax applies when a trust skips a generation — for example, leaving assets to grandchildren instead of children. The GST tax runs at the same 40% top rate as the estate tax and applies to amounts above the lifetime GST exemption ($13.61 million per person in 2025).
On a $20 million trust that exceeds the exemption by $6.39 million, the estimated GST exposure is $2,556,000 — before the trust has even paid a single beneficiary. This is why families building very large trusts often work with an estate attorney to allocate GST exemption deliberately, rather than letting the tax default.
Trustee Fees Matter More Than They Look
A 1% fee sounds small, but compounded over decades it quietly consumes a large share of growth. On a $2 million trust earning 8%, dropping the trustee fee from 1.5% to 0.5% adds roughly a full percentage point to the net growth rate — over 30 years that difference can add hundreds of thousands of dollars to the final balance and the payouts it supports. Compare fees before you appoint a corporate trustee.
Examples
Example 1 — A modest educational trust. Grandparents fund a $500,000 trust for a grandchild's college and first home, expecting 7% returns, distributing 4% yearly, and paying a 1% trustee fee. After 20 years the balance grows to about $742,974, and the grandchild has received roughly $485,947 in payouts — enough to cover tuition, rent, and a down payment without draining the principal.
Example 2 — A large multi-generational trust. A family places $2,000,000 into an irrevocable trust, assumes 8% returns, distributes 5% annually, and pays a 1.2% trustee fee. Over 30 years the balance grows to about $3.42 million while beneficiaries collect roughly $3.93 million in total distributions. Because $2 million is well under the GST exemption, no generation-skipping tax is flagged.
Example 3 — Stress-testing an unsustainable payout. On the same $500,000 trust, raise the distribution rate from 4% to 8% while keeping a 7% return and 1% fee. The net growth rate turns negative (−2%), and instead of growing, the balance shrinks every year. Within a couple of decades the trust is on track to exhaust itself — the calculator makes that failure visible before it happens.
Example 4 — A GST-triggering fortune. On a $20 million trust, the portion above the $13.61 million exemption is about $6.39 million. At the 40% federal GST rate, the estimated exposure is $2,556,000 — a clear signal to consult an estate-planning attorney before funding.
FAQ
How is a trust fund payout calculated?
The annual payout is the trust balance multiplied by the distribution rate you choose. For example, a $500,000 trust with a 4% distribution rate pays $20,000 in the first year. Because the balance grows or shrinks each year, the dollar payout rises or falls along with it, which is why the calculator projects year by year rather than using a single flat number.
How long will a trust fund last?
A trust lasts as long as its net growth rate stays non-negative. If the annual return equals the distribution plus trustee fee, the balance holds steady indefinitely. If the return is lower than the payout plus fee, the balance declines each year and eventually reaches zero. Lowering the distribution rate or the trustee fee is the fastest way to extend the trust's lifespan.
What is a sustainable withdrawal rate for a trust?
Many planners start with a 4% annual distribution, mirroring the rule used in retirement planning. That rate historically lets a diversified portfolio support payouts for multiple decades while the balance keeps pace with inflation. Pushing above 5%–6% raises the odds that the trust will be depleted, especially if investment returns underperform.
What is the GST tax and who pays it?
The generation-skipping transfer (GST) tax applies when assets pass to grandchildren (or others at least 37.5 years younger than the donor), skipping a generation. It is levied at the top federal estate rate of 40% on amounts above the lifetime GST exemption — $13.61 million per person in 2025. The trust itself or its beneficiaries generally bear the tax, which is why large family trusts are structured with legal guidance ahead of time.
Are trustee fees tax deductible or negotiable?
Trustee fees are often deductible as administrative expenses of the trust, but whether and how depends on the trust type and your tax situation. The fee itself is negotiable: corporate trustees commonly charge 0.5%–2.0% of assets, and the difference between a 1% and a 2% fee compounds into a very large sum over decades. Always compare two or three trustees before appointing one.
Does this calculator account for investment taxes and inflation?
This model projects the trust balance using a single expected annual return, distribution rate, and fee, and it applies the GST tax on principal above the exemption. It does not separately model capital-gains tax inside the trust, state-level taxes, or inflation. For a full picture, pair this estimate with a tax professional and use a conservative real (after-inflation) return when entering the expected growth figure.
Disclaimer
This trust fund calculator is provided for informational purposes only and does not constitute legal, tax, investment, or financial advice. Projections are estimates based on the inputs you enter and a simplified year-by-year compound-growth model; actual trust performance, returns, fees, and tax outcomes will vary. The generation-skipping transfer tax figures use federal exemption amounts and the 40% top rate and do not reflect state taxes, future law changes, or individualized exemptions. Trust taxation and structuring are complex — always consult a qualified estate-planning attorney, CPA, or fiduciary advisor before establishing or funding a trust.