About Grow My Interest

Grow My Interest started as one tool -- a compound interest calculator that turns an initial deposit, an optional regular contribution, an interest rate and a compounding frequency into a final balance, total interest, effective annual yield, a year-by-year table and a growth chart. It launched as a single page on purpose, and has since grown into a small set of calculators built around the same math, each aimed at a specific, real question people search for.

The formulas it uses

Standard, published compound-interest algebra: A = P(1 + r/n)ⁿᵗ for a lump sum, P·eʳᵗ in the limit of continuous compounding, and the ordinary/annuity-due future-value formulas for a regular contribution added at the end or start of each period. Annual Percentage Yield follows APY = (1 + r/n)ⁿ − 1. None of this is original research -- it's the same math a textbook, a bank's disclosure, or the U.S. government's own investor.gov calculator uses. The full derivation and a worked example are on the calculator page itself.

What it doesn't do

It doesn't know your tax bracket, account type, or your bank's exact crediting schedule, and it assumes a constant rate and a constant contribution amount for the whole term (aside from the optional annual step-up you can turn on). It isn't investment, tax or financial advice -- see Terms.

Calculators live today

• APY Calculator -- convert a nominal rate and compounding frequency into the real Annual Percentage Yield.
• Savings Interest Calculator -- a simpler version built around the savings-account case, daily compounding assumed.
• Daily Compound Interest Calculator -- the same engine as the homepage, compounding fixed to daily.

What's coming

If these calculators keep earning real traffic, the plan is to keep expanding into the closely related questions people search for, each as its own page rather than folded into an existing one:

• Compound Interest Formula -- the algebra behind A = P(1+r/n)ⁿᵗ, solved for each variable.
• Compounding Calculator -- compare compounding frequencies side by side at a glance.
• Compound Growth Calculator -- the same math applied beyond interest-bearing accounts.
• 401(k) Compound Interest Calculator -- payroll contributions, employer match, and a multi-decade horizon.
• CD Monthly Interest Calculator -- fixed-term certificates of deposit with monthly crediting.
• Rule of 72 Calculator -- rule72Years() already exists; a standalone page for the quick-estimate crowd who won't fill out a full compound-interest form.

Who's behind this

Grow My Interest was built and is maintained by Elbert Ballo, who shipped it as one calculator first and only added the pages above once real search data (not a guess) showed people looking for them.

Corrections

If a formula or number here is wrong, email hello@growmyinterest.com.