# Building Marcus Savings Calculator in Excel

I'm trying to do some analysis in Google Sheets which involves putting money in Marcus' High Yield savings account. For some reason, I can't seem to get my numbers to match the values from their savings calculator.

I'm using the value of interest rate to be 2.25%, compounded daily as mentioned here, and the principal being `\$10000`, with `\$100` being deposited every month for a total period of 2 years.

As per their calculator, this results in an interest of `\$507`, whereas with the below formula, I'm getting `\$12949` or `\$549` as the interest using the formula below.

``````FV(2.25%/365, 365 * 2, -100/30, -10000, 0) - 10000 - 2400
``````

Any idea what I'm doing wrong?

The 2.25% is an annual effective rate (same as APY)

``````e = 0.0225
``````

Converting the annual effective rate to a monthly rate

``````r = (1 + e)^(1/12) - 1 = 0.00185594
``````

Compounding the principal, with `n = 24`

``````10000 (1 + r)^n = 10460.2625
``````

Compounding the payments, with `d = 100` and payment at month-end.

``````fv = (d ((1 + r)^n - 1))/r = 2451.9379
``````

``````2451.9379 + 10460.2625 = 12907
``````

In Excel

``````=FV(r, n, -d, -10000)

=FV(0.00185594, 24, -100, -10000)
``````

£12,906.99

``````interest = 12907 - 10000 - 2400 = 507
``````
• @Prakhar You’re welcome. – Chris Degnen Jan 20 at 14:55