I$\text{'}$m creating a loan amortization schedule in Excel with the following assumptions:

Loan Amount: EUR $1,000,000$

Interest Rate: $10\mathrm{.}0\%$ p$.$a$.$

Loan Term: $14$ years

Grace Period: $2$ years

Repayment Period: $12$ years

Loan Closing Date: $31\mathrm{.}12\mathrm{.}2025$

Payment Frequency: Quarterly $($every $3$ months$)$

Number of Periods: $48(12$ years $4$ quarters$)$

Rate per Period: $2\mathrm{.}5\%($quarterly$)$

Fixed Principal Repayment: EUR $1,000,000/48=$ EUR $20,833$

Total Payments: EUR $1,812,500($Principal $+$ Interest$)$

Total Interest: EUR $812,500$

Questions:

$1)$ First Payment Date

Loan closes on $31\mathrm{.}12\mathrm{.}2025$ and has a $2-$year grace period. Should the first payment be on $31\mathrm{.}12\mathrm{.}2027$ or $31\mathrm{.}03\mathrm{.}2028?$ I originally calculated it as $=$EO$($loan$\_$closing$\_$date, grace$\_$period $*12),$ but I feel like I got it wrong.

$2)$ Interest Calculation $$ Days Count

I$\text{'}$m using fixed principal repayment $($EUR $20,833$ per period$).$

For interest, should I include the extra day when counting days between periods?

Example: $(31\mathrm{.}03\mathrm{.}2028-31\mathrm{.}12\mathrm{.}2027)+1=91$ days instead of $90.$If I do this, my total days per year becomes $369$ instead of $365,$ which doesn$$t seem right.Should I include or exclude the extra day?

$3)$ Excel Table Format

My table includes the following columns:

No$.$ Payment

Due Date

Days $($Helper Column$)$

Beginning of Period Balance

Interest

Principal

Ending of Period Balance

Total Payment

Would appreciate any guidance on whether my calculations are correct, especially regarding the first payment date and day count for interest calculations.

Thank you!