Explain How Compounding Interest Actually Works With Your Own Numbers

Compounding interest is described in every personal finance resource with the same compound examples: invest at age 25 and retire rich. The example is always someone else's numbers. This explains compounding using your actual starting amount, your monthly contribution, and your time horizon, then shows you what the Rule of 72 predicts, what a five-year delay costs, and which of the three variables matters most for your specific inputs.

I want to understand compounding interest using my own situation. My details:
- Current savings or investment amount: {CURRENT_AMOUNT}
- Amount I can add each month: {MONTHLY_CONTRIBUTION}
- Expected annual return: {EXPECTED_RETURN}%
- Time horizon: {TIME_HORIZON} years

Explain compounding interest and show me what it means for my numbers:
1. The plain English explanation: what compounding interest is and why time is the critical variable, in [three sentences]
2. My projection: what my pot would grow to after {TIME_HORIZON} years at the stated return, with and without monthly contributions
3. The doubling rule: what the Rule of 72 shows for my expected return rate
4. The delayed start cost: what I would lose in final value by starting [five years] later instead of now
5. The variable that matters most: of [time in the market], [monthly contribution], and [annual return], which one has the most impact on my final number, given my specific inputs