
Compound Interest
We have recently added the following interest related calculators (with formulas, explanation, and sample problems):
Compound Interest
Continuous Compound Interest
Simple Interest
Effective Interest Rate
Interest Formulas

Net Present Value
We have recently added the following capital budgeting related calculators (with formulas, explanation, and sample problems):
Net Present Value (NPV)
NPV Excel and Google Doc
NPV Explanation
Equivalent Annuity
Present Value Calculator
Present Value of Annuity
Profitability Index
ARR Calculator
Capital Budgeting
Understanding the Cost of Credit

Finance Blog
This section of the site is still a work in progress. More will be coming soon!
For now, some additional resources and calculators are as follows:
How to Calculate APY offering a calculator, formula, and example.