Weekly vs Monthly vs Yearly Compounding: Does It Actually Matter?

Two different questions hide inside "does compounding frequency matter", and they have opposite answers.

Hold the annual rate fixed and change how often it compounds: the difference is 81 cents a year on $1,000. Ignore it. Hold the number fixed and change the period — type "2%" and switch a dropdown from yearly to weekly — and the same digit goes from 2% a year to 180% a year. That is the version that matters if you run a family bank, and it is the one nobody writes about.

Both tables are below, computed rather than asserted.

Same annual rate, different frequency

This is the bank question: yours compounds daily, theirs compounds monthly, and you want to know whether that is worth switching for. The arithmetic:

APY = (1 + APR/n)n − 1, where n is the number of compounding periods in a year.

$1,000 at a 4% nominal rate, held one year:

Yearly to daily is 81 cents. On a thousand dollars. Over a year.

Give it a decade and it barely improves:

The whole spread across ten years is $11.55, and look at how it is distributed: going from yearly to quarterly buys $8.62 of it, and going from weekly to daily buys 20 cents. Almost all of the benefit of compounding more often is captured by compounding a handful of times a year. After that you are chasing a limit.

So the standard advice is right: compare APY, not compounding frequency. The APY already contains the frequency. Two accounts with the same APY pay the same, whatever their dropdowns say.

Why APY exists at all

That advice is not just a convention. It is the point of a federal regulation.

The Truth in Savings Act's implementing rule, Regulation DD, is codified at 12 CFR part 1030. Appendix A gives one formula every institution has to use:

APY = 100 [(1 + Interest/Principal)(365/Days in term) − 1]

In the regulation's own words, "Principal" is "the amount of funds assumed to have been deposited at the beginning of the account", "Interest" is "the total dollar amount of interest earned on the Principal for the term of the account", and "Days in term" is "the actual number of days in the term of the account". For an account with no maturity date, the appendix is explicit: "For accounts without a stated maturity date (such as a typical savings or transaction account), the calculation shall be based on an assumed term of 365 days."

Because a savings account's term is defined as 365 days, the exponent becomes one and the whole thing collapses to APY = 100 (Interest/Principal) — the dollars you earned divided by the dollars you put in. There is nowhere for a compounding schedule to hide in that.

Section 1030.3(f) then adds that the annual percentage yield, the annual percentage yield earned and the interest rate "shall be rounded to the nearest one-hundredth of one percentage point (.01%) and expressed to two decimal places." Apply that to the first table and the four percent row set becomes 4.00%, 4.06%, 4.07%, 4.08%, 4.08%. Weekly and daily compounding are not distinguishable in a disclosed APY. They round to the same number.

Same number, different period

Now the other question, which every page on this topic skips because it is about households rather than banks.

A parent running a family bank does not shop for a rate. They pick one. They type a number into a field and choose a period from a dropdown, and those two choices are not independent — the same number means wildly different things depending on which period sits next to it:

APY = (1 + r)n − 1, where r is the rate per period.

Two percent is either two percent a year or a hundred and eighty percent a year, and the only thing that decides it is an unlabelled dropdown. That is a 90× difference. No amount of daily-versus-monthly agonising gets anywhere near it.

This site's own compound interest calculator suggests rates by age, and it is worth seeing what those commit you to when they are annualised:

Those weekly rates are deliberate, not mistakes. A realistic rate on a child's balance produces no visible movement, so nothing gets taught. But "deliberate" and "small" are different things, and a parent should see the annual number before setting it rather than after.

What a family-bank rate actually costs you

Here is the same information as money. Interest paid over one year on a balance held flat, so the figure stays readable — a real balance grows and gets spent, so treat this as the price of the rate, not a forecast:

Two percent a week on a $200 balance is $360 a year. That is not an argument against paying it — it is a teaching budget, and $360 spread across a year to make compound interest land might be money well spent. It is an argument for knowing the number. The calculator has a "check what it costs you before you commit" section for exactly this reason; this table is the sourced version of that argument.

What a real savings account pays

For contrast, the durable figure. The FDIC publishes a monthly national rate for deposit products. As of 20 July 2026 the national rate for savings accounts was 0.38%, with interest checking at 0.07% and a 12-month CD at 1.68%. The FDIC defines that national rate as "the average of rates paid by all insured depository institutions and credit unions for which data is available, with rates weighted by each institution's share of domestic deposits."

The advertised top of the market is a different animal. In early August 2026, rate trackers put the best widely available savings APYs at roughly 4.10% to 4.15% — Bankrate's savings rate table listed a 4.15% top rate on 10 August 2026, and a Yahoo Finance roundup published the same day headlined "up to 4.10% APY". Those move constantly and are a snapshot rather than a fact about the market; the FDIC series is the one with a methodology and an effective date attached.

Either way, the gap between a real account and a family bank is not a matter of degree. 0.38% a year against 67.77% a year is not a rate difference, it is a difference in what the number is for. One is a return. The other is a teaching device funded out of your own pocket, and running the ledger honestly matters far more than the rate you pick.

The short version

• Choosing between real accounts: compare APY and ignore compounding frequency entirely. It is worth 81 cents a year on $1,000, and APY already contains it by federal definition.
• Setting a rate yourself: the period matters enormously. Convert to an annual figure before you commit, with (1 + r)n − 1.
• Either way: the amount saved each week moves the balance far more than the rate does over a childhood. Run both and see which lever is actually doing the work.